But has George Lucas confirmed any of this?

The Original Vader Is Back
David Prowse, who played Darth Vader in every scene except the one where they took off the mask has stated that he will be back for EPISODE III. This, along with the previous rumor that James Earl Jones has already signed to do a few lines, certainly seems to point to the appearance of a full costumed Vader in the film. If memory serves, however, Prowse had just had hip surgery as of Celebration II back in May, and was still walking with a cane. It’s possible that what we will see of Vader will be just at the very end.