I've ventured there... I have 2 Cayuga ducklings at the same time I have four chicks. First I had them in the same brooder, with a hardware cloth divider so they could see each other and get to know each other, without those ducky webbed feet stomping on any chicks. But the ducks grew so fast I had to give them a second brooder of their own.
Ducks put their growing energy into body size, whilst the chicks put it all into feathers. By the end of the first week, the ducks were more than twice the size of the chicks. By the second week, four times the size. I'm not kidding.
The chicks spread lovely wings, the ducks still had those silly little winglet arms, all fuzzed all over. No feathers yet. But they were HUGE in comparison to the chicks.
MUCH more frequent bedding changes in the duckling brooder.
And I've never filled a dishpan full of warm water for swimming practice for chicks, either.
Love 'em all. They'll be in the same run with everybody, but I'm building a small duck house because I don't want to clean the New Big Coop as much as it would need with ducks living in it. That's the PLAN, anyway. We'll see where the ducks decide they want to sleep.... unless I force the issue. Hmmmmm.