One thing to watch is the mineral you supply. Some cattle minerals can be harmful to other species. Most of the bags have a warning label. There is quite a bit of research on the benefits of mixed species grazing. The Stockman Grass Farmer publication has lots of articles and info on the subject. You can also search NC State University Extension for some good info.
Be careful with sheep and minerals/ grain for cattle and other animals. Most are lethal if consumed by sheep. As stated above check the labels carefully.
We have lots of critters running together on any given day. As long as it's not predator and prey and they get along most mingle well together. Of course there's always a few who refuse to get along Be sure everyone is healthy and vaccinated. Some diseases are transferable between species.
Careful with donkeys. We had one we planned on using to protect the herd and this little bugger killed anything he could. Feral cats, chickens, dogs, foals, calves, goats. You name it. Even tried killing a 800 pound heifer. Pinned her in the corner of a field trying to kill her till she rolled the fences down and escaped before we could get to them.
I put a young ram in a padock with our stud bull and it kept charging and headbutting the bull knocked itself out twice before I could catch it again to get it out obviously a very stupid sheep my bull didnt appear overly phased at the time I think it would depend on the bull and size of the field .