As I said putting him in ROTJ as he is was a fan service of the lowest order.
I could see why he turns up at Jabba's now and then it's a great place to pick up work as well as social diseases at least with the Boba Job scenerio it's a fan service with a purpose (he has something to do which is pretty similar to what he does so well in ESB).
He's the Blackadder of the Star Wars universe, IMPs on the top REBs on the bottom and Fett in the middle making a fat pile of cash out of both of them.