User blog comment:Uskok/Barbossa the Privateer/@comment-4898132-20110531233736

He probably gave "his word" that he would serve him. Maybe by telling him about all of Jack's secrets(not including ones from the Brethren). He probably even heard that rumor of Jack recruiting a crew in the Captain's Daughter and had plotted Jack's capture...even having the court mistake Gibbs for Jack. :O

I'm not 100% on all of that, but it's just a thought.