At this map you can find a few neutral necromancers together with two neutral ghouls. Those ghouls are clearly belong to those necromancers, because when you pick up them, you also pick up those ghouls.
The problem is, when I located them, necromancers join me, but ghouls stayed neutral. They follow necromancers everywhere attacking my defences and creatures, while my defences and creatures ignore them completely. Thankfully, they can be killed by lighting spell.
Basically, looks like if in the map editor you create neutral ghouls, they will remain neutral forever.
Customer support service by UserEcho