This was canon. I suppose it still is, at least as part of the Expanded Universe.

http://viooz.ac/movies/15116-the-star-wars-holiday-special-1978.html

Apparently even George (who claims he had very little to do with it) wants to make this go away.

As he should. It was crap of the worst kind. Mark Hammel had more makeup than Carrie Fisher. She sang badly. It was drivel no better than the Zahn novels.