Anything is allowed to run in 4400 since it is an unlimited class as long as it meets the safety requirements. In fact the winners of the lower classes get an automatic entry into the 4400 race each year,
although I don't think a 4600 car has ever attempted the main race.
The UTV class is essentially an unlimited class, the only restriction being that the engine cannot displace more than 1.0L and must be powersports-based, not automotive (you can't run a Ford 3 cylinder 1.0L Ecoboost for example). Everything else is free game.
The Roxor as you well know, but insist on trolling, is a UTV in name only for regulatory reasons in the United States, and uses a 2.5L engine and automotive drivetrain. Therefore it doesn't qualify for the UTV class. It is sold and used as a road-going vehicle in India under the name "Thar," and foreign market vehicles are legal. Of course none of that really matters, because whatever Dave Cole says goes, and he said Roxors are legal in the stock class (no other "UTV" is)
Yes, the EMC course is only 2 laps and ~150mi total each year (one mostly desert, one mostly rock trails) and the 4400 course is 3 laps and ~200+mi each year (one desert, and two in the rocks). There are also bypasses for the 4600 class on the EMC course for some of the hardest rock trails. I am not sure what the deal is with the UTV course since I've never really followed that class.