Maybe?

The cardboard itself I think is fine, though the unfinished nature of the surface would lead me to be concern with dust that can give your snake some problems.

But...

As long as they stay dry, don't have anything nasty on them from whatever they were packaging, don't have any nasty release from the molding process, don't have anything nasty from sitting on the floor, don't have anything nasty from the rest of the trash, don't release any dust, don't fall apart, and then actually stay upright long enough to function as a hide. You should be all set?

But I would probably avoid them.