Yes, they are dealer special Camaros, just like Scuncio and Baldwin-Motion.
However, there is a difference between Yenko Camaros and some other dealer hotrods- I don't know which ones for certain.
Many (if not all?) Yenkos were ordered under COPO 9561 to have a factory big block. Other dealers installed them after final assembly.
http://www.yenko.net/features/featurecars.htm
http://www.yenko.net/dealers/berger.htm
http://www.yenko.net/dealers/dana.htm
http://www.yenko.net/dealers/harrell.htm
http://www.yenko.net/dealers/motion.htm
http://www.yenko.net/dealers/nickey.htm
http://www.yenko.net/dealers/yenko.htm