The fell bats not being battleline is a huge plus, as if they were they would be a total liability giving away broken ranks whenever the opponent didn't have a better battle tactic to choose. As it is, I think they are a good unit - they are fast and cheap, and can deploy from the grave to pinch and uncontested objective.
The vargheists... Yeah, it would be cool if they became battleline under one of the bloodlines. They are a unit that I can't quite get to work. They are *sort of* vampires, but don't get The Hunger, which is sad. And because they are not summonable, you can't buff them with Crimson Feast, or heal them with Invigorating Aura/Deathly Invocation or bring them back with Endless Legions... They aren't useless, but they could be much better with either the Vampire of Summonable keyword!