How does making BH faction-specific make it like WoW? If you remember, all classes can be played by both factions in WoW. Being like WoW would actually mean BH was available to both Republic and Sith.

Bounty Hunter for Sith works for me, since the Republic has morals, they wouldn't stoop to hiring hitmen to further their goals. Everyone knows that in the SW universe the Sith are evil. There's no sugarcoating it, and Murderers-For-Hire fits with alignment.