Spoiler details

[wish_monger]

 Brimstone is a resurrectionist. What this means is that he conjures new bodies for the souls of his slain brethren to live in. Upon death, the souls are collected from the battlefield and brought to Brimstone, who then transfers them to their new bodies.

This process is completely voluntary which is why he doesn't feel like your typical necromancer; i.e. no miasma of evil or malignancy.