XmlQuestNPCs can talk to ghosts. So only dead players would trigger them, but they couldn't get a questbook, so the QuestNPCs would have to assign an XmlAttachment to the player. You can still follow the Xmlspawner tutorials for setting up quests and NPCs, the only difference is allowing the NPC to interact with ghosts, which is a setting you can have.
Have you eliminated corpse decay on your shard too btw? Otherwise that would be an issue facing players as well (running around on a quest while their corpse decays into nothing).