I had Toyo M55's on the rear of my dually, and HT's on teh front! With the GM locker, I went just about anywhere I wanted to go in RWD. Even up some of the passes, when I was supposed to have chains on empty! Did the same with my 96 sw 3500 too!
Reality is, YES there are some places a dually will not do as well as a rig with a single tire the same width as the duals. With proper planning etc, you will get to where you want to go. There are plenty of Class A and C rigs at local ski area's, as there was with 5W's, TC's or a TT like I did for 12 seasons driving all around the NW using the trailer as a ski hut!
As Bryon mentions, get chains, tires on the std to aggressive AT end of things, or a mild traction tire all around do help in many conditions, But not needed. CHains in snow will get you anywhere, and stopped!!! Too!!!!!
Marty