Anthony Daniels had told me that he had shot a scene with him outside the cave looking in, but that he was the only actor in that shoot. George Lucas himself had beeped R2's "dialogue" which C-3PO reacted to.
This was done very late in the production when they shot the scene with the droids walking towards Jabba's palace. It was a last-minute idea.
The whole scene, though.. I call bullcrap! I am convinced that Luke's obscured face is from another shot. Why else would they show him with the face dark and the hood up? I came to this forum, hoping that some expert on the ROTJ footage could identify it.
Mark Hamill has told us fans at numerous times, in a live fan interview at Hyperspace's forum several years ago and in person to several fans that he did not remember shooting the scene.