I can certainly see both sides, but I think like a lot of other things, it depends on the individual animals as much as anything. A lot of people told me I couldn't keep my pot-bellied pig in with my horses, but he lived with them for years, and even slept in a stall with my mare. He and my mare were such a bonded pair that Pigpig died only about a month after she did. (they both were getting up there in age). I have no doubt though, that he'd have been around longer if we hadn't have lost her.
"Keep a leg on each side and your mind in the middle"