I have been following this thread and I think I have the same bug, I can't make any progress with Onmund after I completed the first main quest. I also used a save where the main Skyrim questline had been completed, so it is probably because of that? I don't have an option to give him any gifts either. It's a shame since I've already played a lot on this save, but I will make a new character and play through it all again to see if it works when I have the time.