That's either a very heavily modified GTR or the dude in the Veyron is just taking it easy. Off the line, maybe the GTR launch control (although the Veyron has its own) and lower weight might give it a little advantage, but once they are over 100mph, 1000 hp will stomp on 480 hp. There would just be no contest.

Edit: More info at http://www.zercustoms.com/news/Switzer-Nissan-GT-R-vs-Bugatti-Veyron-Video.html :

"The Switzer Nissan GT-R is equipped with the tuner's P800 power pack which get Godzilla to a total output of 800 hp and 700 lb-ft of torque."

Even so, 200 hp is a pretty big deficit from a running start as in the second clip. I'm still skeptical.