You can definatly house calls and larger ducks together. Ducks unlike chickens are rarely agressive until it comes to mating and hatching. If you are housing a call drake with a larger drake along with some females, you may be at slight risk. but otherwise you should be ok.
I really don't recommend it for most people. If the birds are all fully grown, you have a large enough area, multiple feed and nesting areas, and your duck to drake ration is good- then you should be fine. For most people though it is safer to keep them separated. It may be rare to have problems, but problems can equal dead ducks. One time I recommend never mixing them is when they are ducklings after the age of about 2 weeks old. As adults though, with adequate precautions, you can sometimes do fine with mixing them.