Yes, it unequivocally does. Sheol is not the place of dead, rotting, physical bodies, nor is it the place of the spiritually dead. It's the place where the souls of the dead are. There is no pragmatic interpretation of this scripture other than the one that says that the dead are entirely unconscious.
Is Everything Vanity?
Ecclesiastes falls under the genre of wisdom literature, a genre of literature common in the ancient Near East. It's one of three wisdom books in the Bible, the other two being Proverbs and Job.
It opens by telling us that these are the words of qoheleth(קֹהֶ֫לֶת, which just means a collector of words/sayings who speaks them in public), the Son of David, king in Jerusalem. There are many theories as to whom the identity of this qoheleth is(many saying it is king Solomon), but the identity is not vital to our discussion. It then tells us the words of the congregation;
Ecclesiastes 1:2 "Vanity of vanities, says the Preacher, vanity of vanities! All is vanity."
The English translation "vanity" is an unfortunate one, to say the least, especially considering that the author uses it over 40 times in the book. It indicates to readers that what the author is saying is that everything is pointless and meaningless; this couldn't be farther from the truth. The word used there for "vanity" is hevel(הֶ֫בֶל), and it does not primarily convey meaninglessness. Its primary meaning is smoke, vapor, or breath. So, what does smoke have to do with life? Well, like a smoke, life is beautiful and mysterious; it takes one shape, and before you know it, it takes a new shape. And smoke even looks solid, but try to grab it, it slips right through your fingers! It's the same with life at times. You think everything is handled, that you're the one in control, and when you least expect it, life slips out of the grasp of your hands because you can't control where it goes. And when you're stuck in the thick of vapor, like in a fog, it's difficult to see clearly. It's the same when you're burdened by life's problems when it's just so hard to see through the thick fog to find meaning.
Modern translations have lost the metaphor by translating הֶ֫בֶל as meaningless, but the Ecclesiastes isn't saying that life has no meaning; rather, that the meaning of life is never clear! Like smoke, life is confusing, disorienting, and uncontrollable. The book is by no means telling you that the things you do have no meaning or purpose, rather that you can never know with certainty where they're going to lead you. It's not saying that the reality of the world is that it's worthless, just that the worth is so perplexing and difficult to find and get a hold of; it's not that life actually is pointless, but that it's unpredictable and uncontrollable nature can leave you feeling like it's pointless. This is a fact of life that no one can argue with. This book is not an atheist's book; it's an every human on earth book. If you tell me that you've never felt like life is meaningless before, then I know you are lying, because every human who has ever lived has. That is the mere fact that the book is trying to convey. So, when you see "meaningless" in your translations, don't think that the book is telling you that life is, in reality, meaningless, because that would go against the rest of what the Bible says; rather, think that it's telling you that life is perplexing and unpredictable, such that at times it can leave you believing that there's no point to anything. This does not go against anything that the Bible says. It's recorded in the Bible that Elijah, a righteous prophet, had suicidal thoughts(1 Kings 19:4)! If that man did not thoroughly believe that life was pointless at that moment, then no one does! So, no, Ecclesiastes does not oppose the Bible when it says that life, wisdom, etc. is הֶ֫בֶל.
Does Ecclesiastes Support the Sadducees?
Does Ecclesiastes 9:2-3 deny the resurrection? No.
Ecclesiastes 9:2-3 "All things come alike to all: there is one event to the righteous and to the wicked; to the good and to the clean and to the unclean; to him that sacrificeth and to him that sacrificeth not; as is the good, so is the sinner; and he that sweareth, as he that feareth an oath. This is an evil in all that is done under the sun, that there is one event unto all: yea also, the heart of the sons of men is full of evil, and madness is in their heart while they live, and after that they go to the dead."
Notice this scripture does not state that death is the one and only event that all people share, but that death is one event that all people share, i.e. that death is the minimum event that all humans share in participating in.
To illustrate with a simple statement; "I and my wife going to Disneyland is the one thing we will certainly do together." Does that statement imply that going to Disneyland is the one and only thing me and my wife will do together on our vacation, thus excluding the possibility that we share in any other events? It's possible to interpret it that way, but you could also interpret it to mean that the event of me and my wife going to Disneyland together is the minimum of events we will participate in together. Such an interpretation does not forbid us from participating in any other events together.
Death being one event all humans participate in is not mutually exclusive with the event of all humans being resurrected. To be clear, I am not interpreting V3 idiomatically. I am showing why Ecclesiastes 9:2-3 saying that death is "one event" that all share does not necessitate that we interpret it as the one and only event that all share(in fact, it seems that interpreting the text in such a manner is more idiomatic than not). It can just as easily be interpreted as the minimum of events that all people share in participating in, or simply one event that all humans participate in, with no reference to the happenings(or lack thereof) of any other events(e.g. the resurrection). That is the plain reading of the scripture. It is not necessary to take it as saying that death is the only possible event all humans share, excluding the resurrection in the process. Thus, Ecclesiastes 9:2-3 does not contradict the resurrection in any manner.
Is There Any Other Way?
There are two moments in Ecclesiastes 9 where the author tells us something about the knowledge of the dead.
Ecclesiastes 9:5 "For the living know that they will die, but the dead know nothing. They have no further reward, because the memory of them is forgotten."
Ecclesiastes 9:10 " "Whatever your hand finds to do, do it with your might, for there is no work or thought or knowledge or wisdom in Sheol, to which you are going."
Ecclesiastes 9:5 is a little more ambiguous than 9:10. Does the author mean the spiritually dead? Does he mean dead, rotting, physical bodies? Many have tried to interpret it as such. Ecclesiastes 9:10, however, cannot under any circumstances be taken to be talking about dead bodies/spiritually dead. Why? Because it says that there is no knowledge IN Sheol, which is incontrovertibly the place of dead souls. Ask any reputable scholar or assess any Hebrew concordance.
But I know what you are wondering... How do we know that when the author says, "there is no knowledge in Sheol", he does not mean, "there is no knowledge being acquired about the earth and its happenings in Sheol"? After all, the previous verses before V10 talk about the earth.
Ecclesiastes 9:7-9 "Go, eat your bread with joy, and drink your wine with a merry heart, for God has already approved what you do. 8 Let your garments be always white. Let not oil be lacking on your head. 9 Enjoy life with the wife whom you love, all the days of your vain life that he has given you under the sun, because that is your portion in life and in your toil at which you toil under the sun."
So, shouldn't that imply that in verse 10, when it says "there is no knowledge in Sheol", it is actually talking about not having knowledge about life and about what occurs on the earth? No. Allow me to illustrate with a short story about a man who wanted to order some pizza...
Man: Hello, I'd like to order one large pizza.
Pizza guy: Hello sir. What toppings would you like on your large pizza?
Man: I'd like pepperoni, chicken, mushrooms, and onions.
Pizza guy: Ok, I've got it. Anything else, sir?
Man: I'd also like 4 pieces of garlic bread.
Pizza guy: As a topping on top of your pizza, correct?
Man: What? No, I don't want it as a topping.
Pizza guy: Mmmmm, no, I think you do. You see, the context of you asking for garlic bread was asking for pizza, therefore when you asked for garlic bread, you were actually asking for garlic bread on top of your pizza.
Man: What? So what if I was asking for pizza before I asked for garlic bread? The subject had changed. At first, the subject was about pizza, and now, it's about garlic bread. Me asking for pizza before asking for garlic bread does not warrant you to interpret my plain statement, "Can I have 4 pieces of garlic bread" as "Can I have 4 pieces of garlic bread as toppings on my pizza." If I wanted the garlic bread as toppings on my pizza, then I could have very easily said, "Can I have the garlic bread on top of my pizza?" But I didn't say that, did I? It's almost as if I didn't want you to put the garlic bread on top of my pizza, and that's what I didn't ask you to. So I ask, stop adding words into my mouth.
Pizza guy: Mmmmm, no, you were talking about pizza toppings before you started talking about garlic bread, therefore you want the garlic bread on top of your pizza. Simple as that.
Man: hangs up
I hope this story illustrates to you just how utterly absurd it is to say that "there is no knowledge in Sheol" actually means "there is no knowledge about the earth and those living on it" simply because what came before the statement was about the earth and those living on it. The subject of what the author was writing changed(who knew that was possible?). At first, the subject was the living/life, and then, the subject changed to the dead. There's no rocket science here. If the author wanted to say "there is no knowledge about life/the living in Sheol", then the author could have easily said that. But he didn't. It's almost as if the author didn't want you to think that "there is no knowledge in Sheol" means "there is no knowledge about life and the earth in Sheol", and that's why he didn't say that. So I ask, stop adding to scripture what clearly isn't there. Paul warns us about that in 1 Corinthians 4:6.
1 Corinthians 4:6 "I have applied all these things to myself and Apollos for your benefit, brothers, that you may learn by us not to go beyond what is written, that none of you may be puffed up in favor of one against another."
Ecclesiastes 9:10 straightforwardly says what it says, i.e. that those in a state of death in Sheol have no work, no device/thinking ability, no knowledge, and no wisdom, end of story; plain and uncomplicated(I didn't say plain and easy-to-swallow/agreeable). To say anything otherwise would be to go beyond what is written(i.e. to add to scripture what clearly isn't found), which, once again, we are warned about by the apostle Paul.
Paul's words at 1 Corinthians 4:6 even seem like a precursor to Occam's razor. While we could posit that the correct interpretation of "there is no knowledge in Sheol" is actually "there is no knowledge of the happenings of the earth or of those living on it in Sheol", it is orders of magnitude more reasonable to simply interpret "there is no knowledge in Sheol" as "there is no knowledge in Sheol", and anything more than that is unwarranted and it makes for a hermeneutically flawed interpretation.
As you can see, Ecclesiastes 9:10 unambiguously and indisputably proves that the dead know naught, neither have they wisdom, thinking ability, or work of any kind, hence corroborating what is told at Ecclesiastes 9:5, Psalm 6:5, Psalm 88:10-12, Psalm 115:17, Psalm 146:4, and Isaiah 38:18-19, bringing everything together in total harmony.