lololoves, I have a friend who has a farm, and she has tons of chicken and ducks that all live together. I think as long as they have their own space they should be fine. You may want to keep an eye on the chickens thou, because she did say the ducks can be mean, even to each other. :(
If the duck hasn't been with them before, it will be the "new" bird and may get picked on by any hen who doesn't like its looks. Chickens establish a literal "pecking order" in which the top hen can peck anyone and never get pecked, and the bottom hen can't peck anyone and can be pecked by any bird. The bottom bird learns to stay out of everyone's way. Ducks sort of do the same thing, but I have no idea where the duck would end up in the pecking order.