What does anyone make of the hypothesis that much of the OT was compiled under the Hasmonean rule?
I really don't know what you are alluding to. Can you be more specific? Who says what about which texts, and on which grounds? The book of Daniel is clearly connected with the Antiochus IV / Maccabean crisis (167/164 BC) which was before the Hasmonean period, and in its Hebrew/Aramaic form it only made it into the last part of the Jewish canon (ketubim), which marks it as a comparatively late book. At that time most of the Torah (= Pentateuch) was probably already translated into Greek. I see little room in the Hasmonean period for anything but marginal additions (e.g. in the Chronicles genealogies, some of which are very late indeed). Or perhaps by "compiled" you mean the formation of the collection itself, rather than the writing of individual works?
Also what do people here make of the prefix 'El' that occurrs in so much of this literature?
'El in some older fragments of OT works is distinct from Yhwh and points to the supreme deity of the Canaanite pantheon, but then "merges" with Yhwh in Israelite henotheism and later Jewish monotheism which are the background to most "Biblical" literature. It appears as a "prefix" and as a suffix in theophoric names of both early and late periods... Again I'm not sure what you are getting at.