The Frequently Asked Questions log was updated today with the following clarification:
MONSTER DEFINED (p. 78 & p. 194): Certain slayer skills and feats only affect monsters. A monster is defined as “an animal, beast, being, or creature not of a playable ancestry.” What about an undead creature of a playable ancestry- e.g., an undead human, undead dwarf, etc. All undead are considered monsters, regardless of what they were in life.
BUMP IN THE DUNGEON 