Allow me to verge of into another theory.

In the book series known as dune, Frank Herbert, the author, created a cult known as the Bene Tlelaxual (sp?). These people, also known as Face Dancers, could revive a dead person by using some cybernetics. This resulted in what is called a Ghola, these mechanical humans lost most of their memory, and only a few bits and pieces remained.

Let us halt for a moment. It seems as though in the world of Final Fantasy 7, they can replace limbs (Gun Arms) and it even seems that Vincent had some robotics installed, because of his arm. Could Hojo have rebuilt Vincent, strong and faster than before? Could Vincent be something similar to a ghola?