I don't think it's cheating, but I do think a carpet floor setup with sliders (something I see a lot) creates a distinct advantage. If you're playing in a situation like that, then by all means slide save it. I personally put all my pins in the rubber casters on concrete floor, so sliding them isn't really possible. I've always thought a carpet sliders setup definitely makes saving the ball easier, but I don't think it's cheating.