All the local Hummer dealers will tell you that you can't use chains or that you must use S-type chains. If you talk with, e.g., Salt Lake City dealers, they will say that they use chains all the time. GM doesn't know squat and keeps referring you to the owner’s manual. I’m a ski patrolman in Southern California, and didn’t need them in the deepest snows of this season running stack tires.
Bottom line, if you use them, is “keep them snug!” Use spanners and drive slowly for 50’ or so and retighten. YOU ARE RESPONSIBLE FOR ANY DAMAGE THEY DO TO YOUR TRUCK!
You may want to see these:
http://www.bb4wa.com/articles/Chains.htm
http://www.flextrax.com/ (see the video)