I am one of the few who successfully keeps ducks and chickens together. I have a pair of Buff ducks with 14 chickens.
I wouldn't attempt to raise them in the same brooder though. The two ducks were a hundred times messier than 25 chicks, daily brooder cleaning was a must. I raised them on a wire floor and they still got water everywhere. I had pans underneath the wire and dumped gallons of stinky poo duck water everyday.
Once big enough they moved in with the chickens and get on really well- no real fighting at all even this last winter when they were all confined together. And very oddly the drake only mates with his duck and doesn't bother the hens at all. I've heard that can be a big problem.
One very important thing is I can't have a waterer in the coop with them because they dump it all over the floor, their waterer is outside in the secure run that they have access to 24/7.
I'd say if you have the space and stuff to keep them seperate, go ahead and try to keep them together. You can always seperate them later if you need too. That was my plan. I was lucky enough to have it work out with them.
ANY bird is messy if kept in improper conditions. For ducks, that means keeping them like chickens. It can be done, if like Ella, you keep two very important things in mind, water needs to be outside, and it needs to be a very small number of ducks. In general, ducks belong outside, not in coops. Remember, they're waterfowl. I agree that you don't want to brood the two together.