I have no experience using vinyl, ceramic, or anything like that, so I do not know whether or not it is safe, the only thing I would suggest is to at least put down paper towels to absorb any elimination. We have to admit, sometimes we do not catch the urine or feces until hours after it has been passed.. at least with my experience, with paper towels the absorption is kept to one side of the tub, leaving the other side rather dry for the snake to retreat to. This way they are not left sitting in their own waste until we change their substrate. If you were to have them only on ceramic or vinyl, I'd imagine their urine could spread around the tub as they moved around. So, no matter what you use, at least put something semi-absorbent to change out when soiled.

Just my own two cents.