Yes, the "hybrid" part of plug-in hybrid is what makes long extension cords unnecessary. You can run off gasoline just like current hybrids whenever you feel like it. I could envision a docking station in my garage that would make it trivial/automatic to plug in the vehicle to top-off the battery pack. And, Hummer designs could carry big battery packs.
Unfortunately the coming plug-in hybrid SUV model that GM CEO Rick Wagoner mentioned specifically is a Saturn VUE, not a Hummer. Hopefully a plug-in hybrid Hummer will follow. Reference:
http://www.usatoday.com/money/autos/...c-saturn_x.htm
Not sure if I'd be interested in the plug-in hybrid Saturn VUE.
Rock crawling on electric power would be super fun and quiet. Stealth mode...
Fun stuff.