I'm thinking scattering the bums or not scattering the bums doesn't matter for getting Carlos as a contact with (minimum of) 3 Fang Points.
Was wearing Weapon - filthy pistol, Offhand - garbage sticker, Shirt - old jacket, Pants - smelly old pants
I killed all gangers I came across, and got Carlos after the fourth time helping the gangers (3 Fang Points).
My stats at the time were Perception 4, Reflexes 3, Strength 1, Will 2
Lack of getting Carlos at minimum Fang Points might be due to low stats. If not RNG, my guess is needing 1 or 2 Will (thematically "presence of self," strength of character).