Yes, Nismo had little or nothing to do the crux of what makes the 'Nismo' Z different from the normal Z.
Autech, who makes the Super GT cars, did the welds, engineered the aero and the installation of the strange body dampers, made by Yamaha, which run horizontally at each end of the car. They are said to be vibration dampers....someone described the function as, 'to keep the unibody from vibrating like a tuning fork'.
Here's a little vid telling about the car.
[ame="http://www.youtube.com/watch?v=QOP-r810Uco"]http://www.youtube.com/watch?v=QOP-r810Uco[/ame]