Nope. There the evil groups you kill throughout the game. Can get a ton of their equipment but thats about it.

You can get relation with them so long as you haven't beat them down too much. (Not hard to do since they are not particularly friendly to start out with.) (Also you can turn your CKO into a cult by capturing the right unique spawns and equipping them as such.) I'll note that I wouldn't necessarily recommend that as they will kill all the merchants coming to your town to help your town grow wealthier, but they will leave your peasants alone and your knights won’t chase them down. (This can be kinda a nice cheat to do in lands far away though to grant your caravans safe passage where your lords are not patrolling.)