The Dark One
Auror
I seem to remember that the contract gave them the final say, but they were happy to use my ideas.I'd expect that from most if not all, small publishers, although I'm sure it would depend on the contract whether they were obligated to give you input.
In fact, I just remembered there was one case (out of six) where my idea wasn't used. The publisher liked my idea but the distributor didn't - so they came up with something else, and I have to admit it was a cracker. Also just happened to be my most successful book, which is a little annoying.