I will add to Matt's comments the following:
In order to be an "official" part of Cruise Moab you must be a member of the TLCA. In order to be a member of the TLCA you must own a Toyota 4WD vehicle...Meet those two requirements and register for CM and then I guess technically you could run any vehicle that would pass the CM tech inspection and meet the TLCA's minimum vehicle requirements
I checked into this for CM 07. My sister-in-law was thinking of coming out with her Jeep
...She owned, at the time, a Toyota 4Runner so technically she could have joined the TLCA, signed up for CM 07, and then brought the Jeep to run the trails with.
Another point to bring up...Breakage. If your buddy were to break something on the trail and become immobile it is unlikely that anyone would have spare parts to get him back "on the road". This was as big of a concern I had with my sister-in-law bringing out her Jeep as was how much ribbing I knew she would take by actually bringing the Jeep out to a Toyota 4WD event