Drakes can be hit and miss with chicken aggression. I keep muscovy, so there may be some differences. I've never seen a muscovy attempt to mate a chicken as they are a bit more lazy about it. I have seen some back and forth between hens of both species, and I've seen 2 drakes be chicken...
I would personally raise the ducklings a bit longer on their own, so they don't become too familiar with the chickens. That can cause problems down the road if you have drakes and they try to mate the chickens.
Ducklings also need to eat a ration formulated for them. You may eventually want to...