This video of the “historic run” clearly shows that the CTS-V had a flying start. Most euro manufacturers testing at the ‘Ring use standing starts for published lap times.
http://cadillac.gmblogs.com/2008/05/the_video.html
The GTR did the same thing. Except the GTR used "cut slicks" to accomplish their "historic time". At least the CTS-V used stock tires.