I would see merc being more towards money grabbers then bounty hunters. I could see bounty hunters patrolling the non house systems when they are not doing any active contracts.
Bounty Hunters file the role of lawful individuals who can go where the police cant.
That is called integrity, not greed. I guess the main thing is modivation and for some reason everyone is under the impression that an ex-criminal would chose bounty hunter over merc.
Cant really see ex-criminals either wanting to join or being allowed to join a lawful organization in large numbers.