This would make an awesome Halloween Special mode :0
For one, for Spook Servant to work, they'd have to win with the faction even if they die, otherwise they wouldn't really have any reason to help -- just to clear that up.
Also, having two conversion roles on one faction is just too much. Spooks will multiply too fast and take over the game, which is pretty fitting, but not as fun. A hardcounter could fix this, but tbh I would say it's better to just not introduce the problem in the first place.
Lastly, Ghosty; still kind of on the fence here, but it seems like a pretty cool hyprid role with a new mechanic. Unique is a good move as well, otherwise it would break pretty fast too. Then again, a role like this plus two converters on the same faction may be just a bit too much.