Though, as an aside, Tyvalir posted on this somewhat recently - we do have some balance adjustments in the pipeline for these guys:
We're planning a few adjustments to ghost-type enemies (particularly their Soul Siphon power) in an upcoming patch. They'll need to be closer to attack, will deal less damage overall, and their channeled attack damage will be spread out over a longer duration.
Nevalistis
NOPE.
Though, as an aside, Tyvalir posted on this somewhat recently - we do have some balance adjustments in the pipeline for these guys: