Yes there were a few instances in singleplayer without cheats where you had illogical combinations of weapons.
The ones that spring to my mind are Jaws' dual AR33's that you can pick up and Xenia's Grenade launcher + RCP90 combo.
Aside from that if I recall correctly the only common dual weapons were the DD44, Klobb, PP7 Silenced, ZMG, Phantom, D5K, and Moonraker. Correct me if I'm wrong...