Hey! I've been just starting to explore necromancy, but it appears that Undead are unable to be "unleashed" via the player tool. The Exact message given is this: "You cannot release this animated creature".
This message is currently given with the following Animations:
- Shamblers, All "Levels"
- Bone Warriors
- Bone Archers
- Goblin Corpses
I'll update further as I continue my explorations.
Updated.