Can she use her "sacrifice a follower" ability on Cursed by a Hag, Poltergeist, etc? Nothing explicitly says that you CANNOT do this, but I'm wondering if that was the intent of the unditchable followers.

I would assume so given the fact that the Vampiress may use her ability on the Hag and Poltergeist as well.

Anything that's a Follower, regardless of it's encounter number or whether it's positive or negative, can be sacrificed. So Hag, Poltergeist, Jester, Deathstalker etc.

Handy ability for those nasty followers

Awesome. Thanks guys.