Integration is another good one I've wondered about in the past. On one hand, as you say, it seems like it's all backed by lore and has clear references to past Elder Scrolls games. On the other hand, it seems like there are demons and Seducers walking around like they're all friends with everyone.
To clarify the mod starts out with like.... 2 Daedra in public areas. 1 is an imprisoned Xivilai, and the other is a Golden Saint outside of the Imperial City. A lot of the daedra and other characters don't show up until much later in the quest line when you do a whole bunch of good deeds to make people less afraid of them. Also a lot of the characters have to pretend to be something they're not like Mazken pretending to be Dark elfs, and Aureal pretending to be High Elfs
As for why Daedra wouldn't be violent.; think about it: there's this big war going on and all the mortals are referring to it as an Oblivion invasion, and you just happen to be stranded in mundus(Cyrodiil). You're massively outnumbered, you don't like Dagon, and you don't really have any issue with mortals. Thus you must find a more subtle role than just attacking whatever comes your way. Most Daedra aren't "animals" they think, reason, have personalities of their own, and they don't always agree with other Daedra even if those other Daedra happen to be the same race as them, or they happen to be the lord that most of their race follow. Granted, just like humans there are some cultural, and physiological tendencies that they might have based on race (ie: like how certain diseases, and mental illnesses run in genes) but as a whole they have a large control over their own personality, actions, and schemes.
As far as I know there isn't much in the lore that would dispute this, and none of this is just thrown in and forced upon you out of the blue.... it's all explained, reasoned, and believable. I mean it's not like random hostile Xivilais will just start hugging you or anything. Integration just brings together the small minority of "weird" Daedra that don't follow those cultural norms.
EDIT: Also worth noting that not all of the Daedra are "friendly" there's still plenty of characters that think they're sooo much better than you and you're just a worthless mortal.... and that's not even counting the Daedra that are openly hostile to you.