Piett: Bounty hunters! We don't need that scum!
Officer: Yes sir.
Notice how the officer says "yes sir" after hearing Piett's comment? Does he actually think it's an ORDER!? That he need to get rid of all the bounty hunters even though it was Vader who summoned them!? Good God!
He's agreeing with him. Rather dismissively, I thought. It's just a polite way to acknowledge a superior officer before blowing him off.