It's perfectly safe to use the bottom of the oatmeal tube for them, but they're likely to chew on their veggie dish. Instead, you might want to go to a dollar store and buy a ceramic dish for veggies and cut the bottom of the oatmeal cannister off, so the piggies have a cardboard tube to play in. As far as the cat ball goes, Percy has one that he plays with occasionally, but he doesn't really chew on plastic much. If you want to use one, put it in the cage or out with them during floor time and see what they do with it. If they push and kick it or pick it up and toss it (this is what Percy does), it's probably safe. If it looks like they are gnawing on it, I'd take it out.
