I'm reminded of the old D&D touch spells where the caster has to roll an attack. Albeit an easier attck because it got to ignore armor.
Anyway, the description of Harm's basic power states that the "character drains the very life from the target with a touch"
Brawling with bare fist is touching. No?
I realize Harm is already being looked at as overpowered, but I don't currently see a reason to disallow it as part of a Brawl attack.