Regular carpet can have fumes in it from the glue that is used. This might sound silly or stupid, but I would take the carpet out and literally sniff it. Put it up to your nose and take a big smell. If you can smell the glue, then don't use it. But if it is an old piece of carpet and doens't have a smell, then I guess it would be the same as using reptile carpet. Same things apply, hard to clean, no substrate to burrow under. You should have 2 or 3 pieces available so you can switch them out, while you are cleaning them. I would worry about mold though. If the carpet absorbed their poop, which it would, I'd imagine, it would be pretty hard to see it and you might miss it altogether and have a nice little colony of mold or bacteria growing. Any reason why you can't use paper towel or newspaper? I mean if you are going to use a non-wood based substrate, those two options would be much better.