My Cats and Ferrets get along well. They enjoy playing together and it's not a concern at all. The ferrets can get a little over-excited but the cats deal with it just fine. They never hurt each other, they let one another know exactly how much they will take from one another.
My Mom has a houseful of cats and a small dog that all stay indoors, they fight sometimes, but nothing major. The dog doesn't care for the cats at all, but only barks and snaps at them if they come too close. Besides, even full grown, some of the cats are much bigger than the dog. LoL!
It all depends on the animals, some will get along, some will not. Just like people really..... :wink: