Zombies could be loaded with simple commands... "Whenever (person) enters the scene, cast this spell or say this thing." They could be used during quests. They could be used as defenses for larger scale battles and wars... Perhaps, even... Skeletons can be assigned a very simple task, while Zombies might be allowed to be assigned multiple tasks. Though they could be easily destroyed. You could even ask them to attack other players, and they would have their own creatures, of sorts... Nothing too fancy, but if you wanted to modify their rituals you'd have to load them with your own creatures. Yet if they are defeated, those creatures become Fenths... You might even be able to possess the most complex of undead creations, moving them and controlling them from afar.
Also, Skeletons should require sticky goop and resin to be combined into a sort of material for the limbs.