One ork probably can't. But since Orks have psychic powers amplified by their numbers, if you managed to convince several orks they could, then throw them out an airlock, they could probably breathe out there. This is generally how I assume 'life support' systems work on a Rok.
Hmm, dis a good question. Tell ya wot, I'll got jump outta a Space 'Ulk an' see if I can breath er not. I'll come back an' tell ya if I ain't dead.
