What kind of rack do you have that can support the needs of both species? Usually the ventilation needed for rats causes issues with humidity for snakes, and I can't imagine how you would keep rats watered in a drawer-type snake rack. I don't know much about the freedom breeder racks they make for snakes, but I'm fairly certain the screen mesh they come with is much too fine to get a water nipple in without cutting it, not to mention the rats won't be able to eat through it.
I would need a little more information before I said with certainty "no, this won't work", but I don't know that there's a reliable rack system that works for both species at once.