Considering the fairly simplistic storytelling of ROTJ, I kinda doubt it. More likely, they just thought it would make a cool little surprise for the audience (or at least the little kids who didn't guess it right away. lol).
I agree too. Carrie Fisher most likely is NO Mark Hamil in terms of voice acting!

And it has been answered in this thread, but yeah, the Breen in DS9 is a complete homage to Leia's bounty hunter getup.