What exactly does he do?  If he is a "process server," he delivers summons and complaints to parties involved in a lawsuit.  The documents come from the court but he doesn't work for the court.  The party who asked for the service, pays him.  When you write "how much he recovers from clients," that makes it sound like he's a collection agency, or it might just be a different way of saying "how much that party  pays him" and making it sound like he's something special when he's not.  Process servers pay SE tax.