A good question.
BH don't "work mainly for the guild". They are the Guild. The guild is not an intergalactic police force - it hunts criminals for money. If a BH attacks you while you're privateering, he should be fulfilling a contract.S trictly speaking a BH can target anyone against whom there is a bounty posted, even unlawful bounties. BUT there is also the fact that the Guild is allied to the police forces of all houses to consider, plus no House would allow an organisation that facilitates the killing of government employees to reside within its zoi. The guild has a station in Manchester - I dont think the BAF Admiralty would want it there much longer if privateers were targetted by the guild. So imho BHers should not take contracts against licensed privateers; hire a merc instead.