The weapons NPCs are using so far:
 
  Resistance
  Assaulter - AR-C, 45/70, AK-47, AK-M, MS16, M16A1, MP5, MP5SD, MP40, MP34, (M9)
  Sniper - AR-CL, 308 Carbine, MBP .50, SA-50, SVD (P226)
  Pistolero - 1911, .44 Magnum, P226, D50, M9, P08,
  Shotgunner - M133 (all), SBS, 1887, SPAS-12 (P226)
  Machine gunner - M60, M249, MG42, M60V
  Rocket - RAT4, RPG7 (1911)
  Hunter - Compound Bow, Recurve Bow (Pistol 1911)
 
  Peggies
  Assaulter - AR-C, AK-47, AK-M, MP5, MP5SD, MP40, MP34, (M9)
  Sniper - AR-CL, 308 Carbine, SVD (1911)
  Pistolero - 1911, .44 Magnum, P226, M9,
  Shotgunner - M133 (all), SBS, 1887, D2 (1911)
  Machine gunner - M60, M249
  Rocket - RPG7 (1911)
  Hunter - Recurve Bow, Compound Bow


Hear is a list of attachments NPCs may spawn with:

(Pistols(so far)
Suppressors
Extended Mags

(SMGs(so far))
Suppressors
Extended Mags
Red dot sight
Reflex sight
Optical sight
Marksman sight
Red dot sight + Extended Mags
Reflex sight + Extended Mags
Optical sight + Extended Mags
Marksman sight + Extended Mags

(Rifles)
Suppressors
Extended Mags
Red dot sight
Reflex sight
Optical sight
Marksman sight
Tactical sight
Enhanced Ranger
Red dot sight + Extended Mags
Reflex sight + Extended Mags
Optical sight + Extended Mags
Marksman sight + Extended Mags
Tactical sight + Extended Mags
Enhanced Ranger + Extended Mags
Red dot sight + Suppressor
Reflex sight + Suppressor
Optical sight + Suppressor
Marksman sight + Suppressor
Tactical sight + Suppressor
Enhanced Ranger + Suppressor

(Sniper Rifles(so far)
Suppressors
Marksman Scope
LongRange Scope
Hunter Scope

(Shotguns)
Suppressors
Red dot sight
Reflex sight
Extended Mags