Energy vampires feed primarily off of life force, and can drink blood if need be, but normally it doesn't sustain them enough. Like when they feed, rather than leaving puncture holes I see it like they leave little burn marks or something because it is raw energy leaving the body... If you want we can change that up =)
And I see dreams like that being able to happened to any witch, they just tend to frequent Lia more because she keeps so much in.
Hope that helps you.