The bumper covers would only solve one of the issues the ML has on really tough trails. Keep in mind that one could run a good portion of the 3 rated trails in Moab without any mods, though a good set of tires is highly reccomended. The trails we ran were 3.5-4+, the toughest trails there.
The big hang-up, literally
, would be the door sills between the weels. Many of the obstacles are steep stair steps like the ones in the picture below. If you had enough tire exposed in front you may be able to pop up on the step but I bet you would get hung up in the middle. My G has a 2" lift and touched in the middle only once. The other G along was a stock '00 G500 and we scraped that on along in quite a few spots. The ML is considerably lower than that. So I would say that no, an ML would have no business on a trail like "Golden Spike".
The lockers are a different story altogether. On these "steps" I doubt the traction control system would be truely effective. Often times you needed full traction from all wheels, right now! Not having that would make for a very dangerous, even life threatening situation. Trails like this can be very dangerous. We do them for the fun of it, and the challenge but, going there ill equipped is not wise.
I think there is a ton of stuff in Moab that would be a blast in the ML. There are a lot of trails out there. The G was developed to thirve in this type of enviroment. Even the G benefits from some improvements on the toughest trails. So IMO the ML would not be a good idea on the couple trails we did. You could try it but, I would expect quite a bit of expensive body damage by the end
