I think, while the rabbits of Watership Down believe in the stories of El-ahrairah, Cowslips warren doesn't (he averted from god). Then, they put their fates in man's hands (they're dealing with the devil). I would say, this brings the christian myth or spirit or how you want to call it, that is part of Watership down, to bear very good.
But generally, I found Cowslips warren in the series very interesting. It looked surreal and unreal, totally artificial.