I think the spacer is to clear the rear Brembo calipers he has.
2008 PBM G8GT, TVS1900, Rick Crawford blower cam, Kooks 1 7/8 Mids, Corsa Cat-back, CHenry Tuned, RotoFab, BP Catch Can, Pedders Lowered Touring Suspension w/ sway bars, CTS-V wheels, Brembos front/rear, in-dash GPS/Bluetooth, de-chromed