The pirates aren't the only one who can claim bounties, any one who attacks the player with a price on their head can claim the bounty.
Yeah, and IIRC, the AI will take bounty into consideration when deciding who to attack. E.g. if an AI is fighting two other factions and you put bounty on one of them, it will most likely influence which enemy is attacked. Obviously all bets are off with human players. If a player thinks they can win, they will attack. Otherwise they'll bide their time and build up additional forces.
With the AI now putting bounties on each other, human players can reap the benefits. Those extra credits might allow for some extra key research or additional trade ports or whatnot. Alternatively, that same bounty can then be transferred into a faction mission for the AI. Tell it to bomb an undefended border world or something, or go after civilian structures.
