I've washed the pillow pets a bunch, and I put them in the dryer. It might depend on the humidity where you live, but I just didn't want to risk the musky smell, or worse- mold or mildew.
I will say that one of them is the dolphin, and that got a tiny hole after the 3rd drying. I think I'll follow the pillowcase suggestion, I'll bet if I had them in there while drying they'd do better. But- there are 3 other pets that have been washed probably 5 plus times and put in the dryer (with the rest of the laundry) and done just fine.