I think the rancor-riding Dathomir witch is a regular unit, not a hero.
Yes, the Rancor riding witch is a regular unit. One of the devs said that somewhere else a couple of weeks ago.
In Ref to the above question about phase III dark troopers, they are confirmed as being in the game (there's a picture of one in one of the screen shots. they're about 3/4 the height of an AT/ST). In one of the other threads about unit scale, one of the petro guys listed the size of each dark trooper unit (I,II, & III) relative to the size of regular storm troopers. The discussion was very interresting, you should look it up.
The dark trooper phase III is in the top left of the following picutre:
http://www.empireatwar.net/media/gallery/screens/june20/large/2.jpg)