I've been a bouncer for two and a half years. We always back each other man, that's just how it's done- it's a job for us, not a proving ground, so we do what we have to to kick the person(s) out. I do try to avoid striking, though.
I would say, however, that those guys were wrong. For one thing, you were already out the door. For another, they should be able to handle someone talking shit to them without jumping on them and getting physical. As a bouncer, you get mouthed an awful lot, and you just have to take it. It should never have come to a physical altercation if the person is on there way out, no matter how much they're shit-talking. They should have let you spout off, grinned, and waved good bye.
Sorry to hear about your nose. Take 'er easy.