I wouldn't really expect him to be there, because he wasn't present in the books or movie... but this Flickr page
has an image of the box for that set, with images of the characters on it. In the lower left they show a handful of guys. There is
one that is tall and black, with something pointy on his head. The Wiki page suggests this is the Mouth of Sauron, but the Witch King had a spiked crown too... on the right we can see a figure (the same guy?) on a black horse, mowing down some Rohan guy. Odds are very high that it's Mouthy and not the Witch-King, but I still wish that image was a little larger.
Regarding actual Star Wars sets... I think the Rancor pit is about all that appeals to me as far as the larger sets go. Unless they went and made something like the Massassi Base. But that doesn't really seem "interesting" enough for LEGO to want to base a set off of.