In addition, the Nine are based on the religions of the Ayleids. (ref: Shezarr and the Divines) We wouldn't have had that Dragon Broke if it weren't so.
edit:
Daedra worship is the stuff done in Morrowind, everything else qualifies as extraterrestrial trade or cult worship. There are no indications of the latter by the Ayleids.
All the city states show a uniform architecture and designs. A fair indicator their culture was rather homogenized.
We have almost no information on Ayeid worship practices, aside from some books. And it's not like Morrowind didn't have an abundance of worshippers of Molag Bal, Mehrunes Dagon, Malacath, and Sheogorath, despite being taboo in their culture. However, Umaril's connection with Meridia and the armor and weapon similiarities suggests that there was some Daedra worship going on. But I never denied that the Imperial pantheon was derived largely from the Ayleid pantheon.
However, it should be pointed out that the Eight empowered the Crusader's Relics, which were made to allow him to face Umaril, so Umaril probably wasn't on too good of terms with the Eight.
As for their culture, it was Herminia Cinna who said this:
My own research into the Late Ayleid Period suggests that there was not a single Ayleid ruler, but many. They were a bitterly divided people, with many warlords vying against each other for power. Their ultimate demise was wrought by their own civil strife at least as much as by the rebellion of their human slaves.
She also wrote http://www.imperial-library.info/obbooks/last_king_ayleids.shtml, which better explains the lack of unity among the Ayleids.