As has been said, the trucks from the original GA and CA sales were sold with SF-97s' that stated "off road use only" and that was supposed to go on the titles as well.
Quite quickly a few folks discovered that some states had no provision for marking a title like that, so they "sold" trucks to owners in that state, got a clear title, then "bought" the truck back with a clear title with no "off road use" on it.
To date, nobody has had issues.
However, I would still urge caution. There have been people laundering grey market Land Rovers in the same fashion to obtain clear titles for vehicle that, like a HMMWV, do not meet DOT/FMVSS specs for the years they were made. I know of at least 2 cases where the owner of such a vehicle got in an accident and then had big heaps of trouble with lawsuits and their insurance provider because they were operating a grey market vehicle that was not supposed to be on US highways.
It is only a matter of time before a civilian owned M998 is in a serious accident- it will be interesting to see if the same legal problems happen there that have happened with Land Rover Defenders running aorund with "clear" titles.