But it only applies to enemies killed with the specialists. Enemies killed with your other party members don't receive the benefit, and, as always, enemies killed with poison or Geo Chains still don't yield HL at all.
Each mob you kill yields a certain amount of cash. The specialist increases that kill cash by a percentage, so the guy has to keep landing the killing blows. (thus hogging all the exp... which might not be bad if you're PLing the guy anyway)
Though by the end you usually have so much money there's not much use for this particular specialist.