Just scoped out the little Hasbro ROTS product booklet (that will be coming with the toys), and in the Mustafar playset section, it refers to the figure that's being included as "Anakin" - twice. No Darth Vader mention.
Likely that the booklet was put together much earlier than the final packaging for the playset though, so I doubt there's anything to it.
Hopefully there are some additional pieces that connect too. Which Insider was that mentioned in? #79? I only have #80 handy...