Gnolls in Blackburrow don't raise warrior faction as far as I know (see, eg,
http://wiki.project1999.com/A_patrolling_gnoll). On my Iksar monk, I killed 1600 gnolls for ~300 fangs, and the turn ins were enough to get me from KoS to apprehensive with the warriors, but I didn't con any shamans, and merchants are still dubious. And yes, the banker is a rogue, and rogue faction is unaffected by the gnoll fang quest.