With enough space maybe... but likly it would be bad for both the chickens, ducks and you depending on your set up. Reason being... Chickens are drier than ducks. Ducks make a mess of water dishes and get coop litter wet. This wet litter is a breeding ground for cocci, a protozoa that can make chickens sick. To maintain the dry ness and the need for head dunking by ducks to clean their nares, you'd be spending lots of time cleaning after them all. Of course it may work depending on set up and if you can keep the chickens dry and the ducks wet so to say.
