First come, first served.

If you're able to kill the hunt mob with your party/raid/fc you're allowed to go for it ... I think some dev said that harrassement only starts if someone tries to reset an already engaged hunt mob.
And sorry, but it's not true: just because we're playing a MMO, doesn't mean you have to wait for the entire server. I played a lot of MMOs with World Bosses etc ... ppl wait long enough until they think they have enough ppl to kill - not a single minute longer.