I'd say it is more than umprobable that the Imperial Council hire the BH Guild for hunting Privateers. But, if they do, some Bounty Hunters, attracted by rewards only, can choose to work for Kusari and hunt Privateers.
We are only talking about Bretonian Privateers and specificaly QCP. IMO, QCP are semi-legal as Junkers or Hogoshas. A BH will do nothing against them in regular circumstances.