This story never got the traction it deserved. There was a second John Doe, who was never identified. The people that worked at the rental truck company said there were two and the investigators originally put out two images, one was the spitting image of McVeigh, the other was pulled. If the rental truck guys were good enough to help produce such a good image of McVeigh, why was the second image pulled.
Yes it appears there were 2 men with the van according to Terry Nichols, this article is by Jayna Davis from 2011. Jayne Davis believes the unnamed terrorist is Middle eastern though.
http://www.americanthinker.com/2011/04/confession_of_the_oklahoma_cit.html
From the Article linked above:
During the interview, the convicted bomber unleashed a startling admission: John Doe 2 exists. The FBI report states, “Nichols advised that John Doe 2’s name had not been mentioned during the (FBI) investigation, and therefore, he feared for his life and his family’s well-being should it become public.”