well, privateering happens outside the house - usually in deep enemy space. - so the probability to meet both, the lawful bret forces and the privateers is rather low.
from the lawful point of view - privateering is an unlawful act, - bretonia is most probably aware of it, but its as tactic in times of war. - i haven t payed too much attention to it - but there have been QCPs in sigma-13 sometimes - some time ago. - if for example someone had payed to have them killed ( most likely a kusari cooperation that wants to ensure that their niobium transports make it safely to their destination ) - bretonia wouldn t complain about them being attacked.
of course, it would NOT be right to attack a privateer in new london, cause THERE - they enjoy the reputation of a fully ranked bretonian officer of the military. - and attacking a privateer in bretonian space should result in the QCO assisting for sure.
either way - its a difficult thing - and hunters ( not only BHGs but also mercs and kusari military etc. ) have to think before pulling the trigger. a BHG that attacked a privateer in non bretonian space should not fear retribution from bretonia in any way though. a BHG that attacked them in bretonian space should be aware that he most probably lost a future customer though.