I have my 4 swedish ducks (young, only 3 months old) and a pair of call ducks (breeding, probably a year or so old) in one large run. I'll get pics tomorrow (it's raining out there today).
Since the breeding drake is older, he is in charge out there, the swedish ducks defer to him (or pay the price in tail feathers,
) It is sort of funny to see this tiny little duck bully the swedish into running away from "his" pool. I had a LOT of swedish in there, he has actually gotten more friendly to them since I cut back to 4 swedish.
I have three call duck babies (so far) and have more eggs in the bator to introduce once they hatch/get bigger. I am hoping they will all get along ok, if not, I may have to segregate.
My pen is new (just finished recently) so it needs landscaping, but it is pretty big, with two areas that are "out of view" of each other - they can go back and forth, just have a corridor that narrows the path down a bit, so they can get away from each other if they want to.
I had to put the food down in the lower area, and a pan of water, so the swedish could eat and drink, even if the call drake was keeping them out of the pool. I have two large dog houses for them, one up top, one down below. I may have to add another if I add more ducks, but for the most part they don't use them except if it is really windy out or if they are layign eggs (only have one female call laying right now).
I would think that as long as the call ducks aren't being bullied, you can keep them together (unless it is breeding season and they try to interbreed) I would just make sure there is more than one source of food and water.
Happily, My setup is such that I can put a fence across the corridor if I need to seperate for breeding season.
meri