Lots of waterers/kiddie pools/ etc. That way the chickens never run out of water because the ducks have used it all up during playtime.
I've heard of male ducks trying to mate with the chicken hens -- don't know if that happens all the time. Haven't seen it with mine, but it isn't breeding season.
The personalities of the ducks/chickens are important too. I had a barred rock hen that took no nonsense from anyone -- she was the boss till the geese grew up. She had even our big Pekin drake in order. But most of the rest of the chickens leave the ducks alone - or get chased away by the ducks. It would depend on how much space you had too . . . if there is enough space I think it would work out okay. We have a raised coop on a trailer and the ducks sleep under the coop, or under the trees and the chickens sleep in the coop -- works out pretty well that way.
Good luck!