Key word there, wet. Besides that, everything passes right through him because he's basically made of sand. Both Smoker and him have shown those traits.I don't remember when, but Smoker was even sleeping at one point and had a punch or weapon pass through him. So yeah Croc is the same. I'll give you that he's made of rubber. But rubber is an ability he was given. The bottom line is that yes he is all rubber so it's like an element, however, since he is able to be cut or burned, technically, not all things can pass through him. Like a logia type. And if you need the actual definition. Heres a site that will clear things up.
http://onepiece.wikia.com/wiki/Logia
If that doesn't convince you then I don't know what will.