Has the exact time frame been pinned down yet? It's a twenty year gap between ROTS and ANH. I wouldn't expect it to be too close to the original film to duck the issue of why we don't see Leia doing her thing, or run into anyone else familiar.
They probably don't want to overuse Vader. The prequels and TCW proved Palpatine goes through a lot of expendable henchmen.
I wonder if a certain pair of droids will show up though.