You also have to consider the sex abuse possibility. Drakes are notoriously aggressive sexually and because of the difference in anatomy can cause serious harm to hens if they can get ahold of them.
You aren't going to want your ducks and chickens sharing a coop. Ducks are messy, make mud, etc. They get along fine in the same area but not the same coop.
Ducks, turkeys, geese, guineas, they all co-exist pretty well.