The NET is apparently translating with the LXX and the Samaritan Torah, against the Masoretic tradition and Onkelos and the Jerusalem Targum. This is a difficult translation in the Masoretic view. The NET choice might be based on the opinion that the LXX and the Samaritan versions reflect an earlier, more authentic tradition rather than on an actual translation of the Masoretic text that the OP quotes.
The Masoretic interpretation
The Masoretic reading is that "lo eloha" is an adjectival phrase, parallel to "lo y'daum" in the second line and "mikarov bau" in the third line, and similar in construction and meaning to "b'lo el" ("with a no-god") in Deut 32:21. So "eloha" is not really singular nor plural in this context.
To be read as "not to God" we would expect "eloha" to have a "lamed" prefix meaning "to" in parallel with the "lamed" prefixed to "shedim" that gives us "to demons". English supports an assumed "to", there being little difference in meaning between "not God" and "not to God", but Hebrew has no such implied "to". You really need the "lamed".
If "eloha" were a corrupted form of "Elohim" in the sense of God then then there would be a problem with the following word, also "elohim", but in the sense of "gods". Juxtaposing these two senses of the same spelling in the same verse would be jarring and would break the thematic unity of the verse which is "useless foreign gods that your ancestors were never beholden to".
Holmstedt's "demons [who] are not divine" is a spot on Masoretic translation, similar to Onkelos's impotent or useless gods,
שֵׁידִין דְּלֵית בְּהוֹן צְרוֹךְ
Gods that are no gods is a common theme, as in the text following the OP quote, Deuteronomy 32:21
הֵם קִנְאוּנִי בְלֹא אֵל כִּעֲסוּנִי בְּהַבְלֵיהֶם
and as in Jeremiah 16:20,
הֲיַעֲשֶׂה-לּוֹ אָדָם, אֱלֹהִים; וְהֵמָּה, לֹא אֱלֹהִים
and as in Isaiah 37:19,
נָתֹן אֶת אֱלֹהֵיהֶם בָּאֵשׁ כִּי לֹא אֱלֹהִים הֵמָּה
and as in the imagery of Deuteronomy 4:28,
וַעֲבַדְתֶּם שָׁם אֱלֹהִים מַעֲשֵׂה יְדֵי אָדָם
אֲשֶׁר לֹא יִרְאוּן וְלֹא יִשְׁמְעוּן וְלֹא יֹאכְלוּן וְלֹא יְרִיחֻן
and Psalm 115:5
פֶּה לָהֶם וְלֹא יְדַבֵּרוּ עֵינַיִם לָהֶם וְלֹא יִרְאוּ
so there is no need to see a possible doctrinal issue here.
When reading Deut 32:15-17 together as a single paragraph broken into two parts, we see a list of actions in consecutive clauses:
- rejected the "Eloha" who made him (15)
- spurned the Rock of his salvation (15)
- made [Him] jealous with foreign gods (16)
- angered [Him] with abominations (16)
- sacrificed to demons, not "eloha"/"Eloha" (17)
followed by a denigration of the gods and demons,
- gods with whom they were not familiar (17)
- new ones, recent arrivals (17)
- that their fathers had never feared (17)
In each of the clauses of the first group there is either an explicit or third person reference to God. The group begins and ends with "eloha", apparently an intentional symmetry. In the second group there is no reference to God, only to the gods and demons. This supports the NET reading.
The spelling of "eloha" in Deut 32:17 is without a "vav" following the "lamed", like the "l'elohim" in Deut 32:3. This form of abbreviated spelling, where a letter representing a vowel sound is dropped, is very common, although it is unique for the word "eloha" (not counting Kings II 17:31, which is probably a copyist mistake). In the case of Deut 32:17 as in Deut 32:3 it is not necessarily a mistake. It might simple preserve an older scribal tradition for this particular verse. There is no cognate basis for taking this spelling as a hint for reading "eloha" rather than "Eloha".
The scribal tradition
The scribal tradition is that the "eloha" of Deut 32:17 is a doubtful instance of a divine name, which means that it must be written with the intent of writing a divine name to be on the safe side. This gives some credence to the NET translation in that it preserves a masoretic understanding that this "eloha" might mean "God".
In the scribal tradition, verses 1-43 of Deut 32 are written in two columns of equal width separated by an empty column of the same width. The total width of the three columns is the same as the width of a regular column of the scroll. The text in each column is fully justified by lengthening specific letters. The reading order is right-to-left, one line from each column (rather than reading all of the first column then the second). Verses can start at the right margin of either column and end at the left margin of either column. No verse fits into one column only. The longest verses require two-and-a-half rows. The longest row of either column is 22 letters, including the letter width spaces required between words. The first clause of Deut 32:17 usually starts in the second (left) column and has 18 characters and spaces. It is one of the more cramped clauses in terms of the lettering because many of the letters are wide letters. However, it is not the most cramped clause and the addition of a "vav", which is a narrow character would still not make it the most cramped. So a typographical explanation for the the missing "vav" is probably ruled out.
Also, the first and third clauses of Deut 32:17 and the first clause of Deut 32:18 all end in consecutive rows the left column, each with a tri-gram, "eloha" (אלה), "ba'u" (באו), and "teshi" (תשי). However, the letters do not form any acrostic nor do the words have any meaning when combined, so this is likely a typographical coincidence rather than an explanation for the missing "vav" in "eloha". There is one run of four left-column ending tri-grams in Deut 32:27-30, that also appears to be coincidental.
The reading tradition
In the reading tradition (Yemenite) the "eloha" of Deut 32:17 without the "vav" is pronounced in exactly the same way as all other instances of "eloha" with a "vav", with the accent on the second syllable, "lo". That is, the dropped "vav" does not affect the pronunciation or move the accent to the last syllable, "ha".
Daniel 11:37-38 contains a parallel construction to Deut 32:17 (according to the Daat Mikra) and contains three instances of "eloha", all of which are references to the gods. The intent is apparently to use well known pejorative language of Deut 31:17 to denigrate the Northern King.
A fragment from Qumran that contains Deut 32:17 could shed light on the question either by showing us an alternative spelling, or by the use of the ancient Hebrew script for "eloha". I know of no such fragment.