Ford will stay with Fusion for 2013 Cup car?
To answer your question - Yes, but I don't think there is a gnat's hair difference in the various "models" regardless of manufacturer being raced these days. Doesn't matter if they paint or stick Fusion, Mustang, Camry, Avenger, Impala, or any graphics on the car - any NASCAR car.
Today most American stock cars may superficially resemble standard American family sedans, but are in fact purpose-built racing machines built to a strict set of regulations governing the car design ensuring that the chassis, suspension, engine, etc. are architecturally identical on all vehicles. Ironically, these regulations ensure that stock cars are in many ways technologically less sophisticated than standard cars on the road. For example, NASCAR (the largest stock car organization in the U.S.) requires carbureted engines in all of its racing series, while fuel injection is now universal in standard passenger cars.
Modern racing "stock" cars are stock in name only, using a body template that is vaguely modeled after currently-available automobiles. The chassis, running gear, and other equipment have almost nothing to do with anything in ordinary automobiles.
The main differences in any models today, IMO, are the graphics, the driver, and the pit crew - last two being the meaningful ones, of course.