Seasons Greetings RMS Friends!
I have personally driven all 3 Hummers. The military version as Rufus points out is extremely difficult to get hung or mired. The civ. version goes down it's own path at AM-General for "cushy civilian" treatment, but at heart is still an H1. The H2, IMHO, is a hummer in name only. It's built on a "GM-RV chassis" and has a standard GM powerplant and about half the ground clearance of the H1 (approx 16in at the differential). The H2 never sees any part of the AMGeneral production facility. It's a wimp. Calling it a baby hummer is being very generous. It's probably what the blazer should have been.
I too have had the bejesus scared out of me while working in the mountains of Mexico where the military H1 of the Mexican airforce scrambled around the mountain paths where our VW microbus couldn't hack it, even attempting to climb grades in reverse.
I suspect that those who rolled their hummers were well outside the design parameters in both angle of attack, and excessive speed. It's been my experience that hummers (H1) are stable and safe when operated with caution and restraint. When operating in testosterone overload mode combined with excessive speed and an attitude of invincibility and a severe shortage of restraint and respect, the outcome is predictable and probably deserved.
I wish all who participate in RMS a safe, prosperous and joyful New Year with Good Health a tolerant spouse (or significant other) and as much fun modeling as you can stand. Bruce