One of my friends breeds rats and he keeps them in a separate room because of the snakes becoming very aggressive, not defensive. His rat snakes are able to smell the rats and go nuts when rats are in the same room as the rat snakes the rat snakes all turn their heads to the cage openings, ready to feed. If you think there might be a respiratory issue though I would keep them in separate rooms. Most people I know who breed rats keep them separate for the purpose that I mentioned though (as far as I am aware). Some species could be less receptive to the rat smell but unless you are okay with an accidental nip I'd advise you to avoid using the same room.