I don't understand why omeluum isn't a valid option instead of the emperor if you meet the criteria that you haven't killed him, sold the ring he gave you, took the ring from him, and if you saved him in the iron throne and meet up at the society.
Omeluum seems to be deeply uninterested in the fight. Ironically, if he was more invested in it, players would probably trust him less. I was disappointed that I wasn't able to speak to him more about mindflayers and the Emperor in particular.