It's odd to me that this isn't literal. The early portion of Genesis (1-11) is usually very literal. In my studies, Numbers is more literal than Gen 1-11 (so literal that I called it "Greek vocabulary on top of Hebrew syntax").
Uses in the Greek
The Greek word appears in the NT three times, all in Hebrews. (All scripture references are from the NASB/NASU unless otherwise noted.)
Hebrew 11:5 By faith Enoch was taken up so that he would not see death; and he was not found because God took him up; for he obtained the witness that before his being taken up he was pleasing to God.
Hebrews 11:6 And without faith it is impossible to please Him, for he who comes to God must believe that He is and that He is a rewarder of those who seek Him.
Hebrews 13:16 And do not neglect doing good and sharing, for with such sacrifices God is pleased.
Interestingly, the word is found several other times in the Septuagint. From those uses, we can see that the Septuagint translators repeatedly used this word for walked. In Genesis 5:24 it also speaks of Enoch. And the same phrase in Genesis 6 (regarding Moses) appears.
Genesis 6:9 These are the records of the generations of Noah. Noah was a righteous man, blameless in his time; Noah walked with God.
The Greek has "Noah pleased God."
Then God commands Abraham to walk before Him:
Genesis 17:1 Now when Abram was ninety-nine years old, the LORD appeared to Abram and said to him, "I am God Almighty; Walk before Me, and be blameless.
The Greek of the bold portion is "be pleasing in my sight." Notice how the Hebrew links being blameless with walking with God.
Genesis 24:40 He said to me, 'The LORD, before whom I have walked, will send His angel with you to make your journey successful, and you will take a wife for my son from my relatives and from my father's house;
The Greek is "in whose sight I have been pleasing."
The same translation idiom, using "pleased" for "walk," appears in Genesis 48:15, Psalms 25:3; 56:13; 114:9, and the apocryphal Sirach 44:16. Sirach 44:16 is a reference to the story of Enoch.
On the other hand, Genesis 39:4 and Exodus 21:8 have forms of the Greek word in question but the Hebrew does not have a word for walk. Instead, Genesis 39:4 has "found favor in his sight" and Exodus 21:8 has "displeasing in the eyes." Those are expected.
In a third category, we have Judges 10:16 where "served the Lord" is translated into Greek as "pleased the Lord." This is a different Hebrew phrase, but the end is the same. That is, serving God does please him.
Uses in the Hebrew
When some other verses use "walk with God" (and similarities) it definitely implies pleasing God.
Deu 5:33 You shall walk in all the way which the LORD your God has commanded you, that you may live and that it may be well with you, and that you may prolong your days in the land which you will possess.
Deu 10:12 Now, Israel, what does the LORD your God require from you, but to fear the LORD your God, to walk in all His ways and love Him, and to serve the LORD your God with all your heart and with all your soul,
Jos 22:5 Only be very careful to observe the commandment and the law which Moses the servant of the LORD commanded you, to love the LORD your God and walk in all His ways and keep His commandments and hold fast to Him and serve Him with all your heart and with all your soul.
1Ki 2:4 so that the LORD may carry out His promise which He spoke concerning me, saying, 'If your sons are careful of their way, to walk before Me in truth with all their heart and with all their soul, you shall not lack a man on the throne of Israel.'
1Ki 8:23 (cf. 2Chron 6:14) He said, "O LORD, the God of Israel, there is no God like You in heaven above or on earth beneath, keeping covenant and showing lovingkindness to Your servants who walk before You with all their heart,"
1Ki 8:25 (cf. 2Chron 6:16) Now therefore, O LORD, the God of Israel, keep with Your servant David my father that which You have promised him, saying, 'You shall not lack a man to sit on the throne of Israel, if only your sons take heed to their way to walk before Me as you have walked.'
2Ki 23:3 The king stood by the pillar and made a covenant before the LORD, to walk after the LORD, and to keep His commandments and His testimonies and His statutes with all his heart and all his soul, to carry out the words of this covenant that were written in this book. And all the people entered into the covenant.
2Ch 6:14 He said, "O LORD, the God of Israel, there is no god like You in heaven or on earth, keeping covenant and showing lovingkindness to Your servants who walk before You with all their heart;
2 Chronicles explicitly states that God shows lovingkindness (covenant mercy) to those who walk before Him.
2Ch 34:31 Then the king stood in his place and made a covenant before the LORD to walk after the LORD, and to keep His commandments and His testimonies and His statutes with all his heart and with all his soul, to perform the words of the covenant written in this book.
Jer 7:23 But this is what I commanded them, saying, 'Obey My voice, and I will be your God, and you will be My people; and you will walk in all the way which I command you, that it may be well with you.'
Mic 6:8 He has told you, O man, what is good; And what does the LORD require of you But to do justice, to love kindness, And to walk humbly with your God?
In these above, those who walk with God are those who are righteous and those who desire to be righteous. We know that righteousness does indeed please God.
We can also see the opposite. Someone doesn't walk with God, and it is displeasing.
2Ki 10:31 But Jehu was not careful to walk in the law of the LORD, the God of Israel, with all his heart; he did not depart from the sins of Jeroboam, which he made Israel sin.
The connection between walking and pleasing God is made explicit by Paul in 1 Thess 4:1 "Finally then, brethren, we request and exhort you in the Lord Jesus, that as you received from us instruction as to how you ought to walk and please God (just as you actually do walk), that you excel still more."
Though he uses a different Greek word for "please," this Hebrew thinker explicitly connects "walk" and "please God." Likewise, in Romans 8, he says that those in the flesh cannot please God. But believers are not in the flesh, they are alive in the Spirit and must act accordingly.
In the rabbinic literature, the rabbinic law is also called halakhah. This means that it is not just a set of laws, but a "path to walk" and live your life by. This should be done not in fear or with an attitude of legalism but because "When you do these things, you are constantly reminded of your relationship with the Divine, and it becomes an integral part of your entire existence" (prior citation).
In conclusion, translating "walked with God" as "pleased God" is justifiable with a caution. We see this first by the examples of those who "walked with God." Enoch, Abraham, and Noah are known for their righteousness. Abraham is even called a friend of God.
The danger in translating "walk" idiomatically as "pleased" is in confusing cause and effect. Abraham and the others pleased God because of their actions. A reader who only had the Septuagint should still realize this as they would be expected to have read more of Abraham's tale and see how the actions God praises are righteous ones (and not his failures). However, it is a danger that the translator needs to weigh.