I'm part of the QCP. If a BH engages me outside of Bretonia, I have no problems with it, but you should really be fulfilling a contract to do so since that's what bounty hunters are meant to do. Where's the payoff for the BH if he's not going to get anything out of the engagement?
If you do attack me, you should expect to be in trouble if you ever enter Bretonia though. I am part of the Queens forces. Therefore you have attacked her, and if you're seen in my patch I will hunt you down with all the force at my disposal. That's the risk a bounty hunter has to take.
I've said it before, and I'll say it again. Bounty Hunters are not a police force. Look at the name. They hunt bounties. If there's no bounty, they shouldn't be hunting.
That said, if I'm engaged in piracy outside of Bretonia, and a BH comes across me, I've no problems with him trying to shoot me up. He should, of course, expect and demand a fee from the trader for his services.
Edit: I don't care if the bounty is only 1 credit, just make sure there is a bounty.