Of course it's possible to dual world. He's asking whether or not you can dual wield two seperate weapons. I.e. a gun and a knife.
Yes. In fact, just to prove it, I threw together a left-hand sword, that can coexist with any other weapon (Unless it uses the left hand as well), and to test, that included swinging that sword at the same time as shooting the default gun. (But couldn't get a decent picture. Got one with the hammer, though. Doesn't really show the movement)
Clearly, it would take some work to make left weapons work as flawlessly as the right side ones, but it is certainly possible.