Hexing doesn’t boost dark property damage, it boosts dark property skill damage (i.e. it doesn’t boost the damage of the zombies’ autoattacks),sadly. It works with every Bokor attack skill (even Bwa Kayiman) but not zombie attacks.
I’ll unsummon them to utilize Gebura/Double Chance, because it’s annoying if zombies attack and use up your debuffs. I guess Kabbalist is the only Class really benefitting from unsummoning because the developers simply couldn’t make an attribute to have these debuffs only trigger on the Kabbalists attacks/skills, much to the grief of every Kabba 2/3 player, especially when there’s a Necromancer/Sorcerer or someone brought his companion along and forgot to switch the autoattacks off 