Steve, the UP rotaries are usually powered by a "snail", an ex F-7B with the traction motors removed but the diesel power plant retained and feeding the traction motors on the rotary. Some of the newere rotaries are self powered, with larger diesel engines and a honkin' big generator that actually turns the rotary plow. It's hard to tell from that video but it looks like one of the newer ones, with the large circular object in the rear part of the generator system.
Josh, great video. I didn't know that the UP ran rotaries out on the plains. At least when the SP was still in charge, every rotary train had one on the front and one on the rear, so they could buck their way out if the front rotary got caught in a drift. They were always run in that configuation over Donner Pass, although I don't know if that's still common practice.