The tow rating is grossly understated to err on the side of caution and longevity. But yes, the tow rating is the total amount of pounds the manufacturer recommends pulling, including the trailer. Whatever you haul, just make sure it's pretty well centered over the axle so that the trailer bears most of the weight. That way all the UTV is really doing is propelling the weight versus carrying it.
My RZR S is rated at 1500 pounds, and I've had a shockingly heavier load behind it a time or two because I had no other choice. Low gear, manage your speed, and you should be fine.