Yeah, right.
Sparco Evo 3 seats are incredibly light, and easily took some of the weight off that car, even with a harness bar.
Autoblog said something similar, except that it didn't hinder performance.
Either way, it's not a stock Caddy, so why should GM try to throw it in the face of BMW whose time was set by a stock M5? The testing part is fine, but I highly doubt BMW or Audi will care they got beat by a car wearing equipment that just so happens to also be racing equipment.
Common sense will say otherwise. It has modifications/non-production materials. It's a modified car as far as I'm concerned unless someone wants to test a M5 or RS4 with similar equipment and get a time for them.