I think I knew that already? I dont' remember haha.
Yes, I have used demonologists to great effect in my Mage build. I used them to help keep my archdemon number high. For severe losses, the rune mage was the big resurrector.
Phantom demonologists so they can summon for mega meat shields (hello summoner level 3 and hello archmage level 3 skill), and before the phantom demonologists disappear, resurrect a few archdemons while dealing damage.
It is nifty since it also does a fair amount of damage too.
Warriors get so much more leadership though, so I wonder how that would fly instead of using a mage.