You can INCREASE your faction for this guy by pre-emptively killing the vampires in the 3 houses related to the quest he gives you in TB Mountains. The camp location is #3 on the EQAtlas map for Teneborous Mountains. You may need to faction here for a while if you are scowling. Each vampire kill is +5 faction for him.
This guy is NOT on the same faction as the rest of the Katta guards. Currently I'm apprehensive to the guards and scowling to this guy. The guards are social with him and will assist him regardless of your faction with them.
Edit to add: After 10 minutes he did not wander back to the guards. He doesn't it very hard. Faction hits for killing him: Johanius Barleou got worse. Katta Castelum Citizens got worse. Magus Conlegium got worse. Nathyn Illuminious got better. Coterie of the Eternal Night got better.
I was still apprehensive to the guards next to him after killing him.