Yeah I suppose, and the Fiends do have the stones to attack Camp McCarren in one of the endings (even if it is unsuccessful).
Forget the ending. Their are 5-7 regular fiend groups I check out when I want weapons/ammo/money. Near McCarran and to the SW.
1) Gang at Vault 3.
2) Group at around Zapps signs to east of Vault 3
3) A couple at pump station
4) A few at Steelworks, fighting Mr Steely/Whatever
5) A group west of Steelworks, near red rail cars
6) Ongoing battle between NCR troopers and Fiends near abandoned warehouse outside McCarran. Maybe half the time 1 dead NCR trooper to loot also
7) A pair of NCR troopers who have killed 1/2 fiends in that area also. I never see the battle, I just loot the dead fiend(s)
I think it takes what? 3 days game time for them to respawn? I love going to vault 3, getting all the clowns to follow me, then running
around the vault building, dropping mines or using grenades at the corners after I take out the melee fighters first.
I don't know who supplies the Fiends, but the Fiends supply me...