Ok, let me clarify.
1 - Was the Bentley Speed 8 an evolution of the Audi R8C?
I could go down the easy way of saying ... yeah, Same Designer/Engineer; Audi engine; Audi money; Audi drivers; Joest Racing (under the "Team Bentley" banner).
But things are never that simple. Can we say that the Bentley Speed 8 was the successor of the Bentley EXP Speed 8, and that this was the successor of the Audi R8C?
Again, let's hear it from the man that designed them all. I'm acting as a lawyer now so I selected the most relevant passages that are useful to prove my point. Feel free to look for the ones that oppose it most
Full interview (a very interesting one) -
http://www.mulsannescorner.com/bentleyelleray.html
2 - Did the Bentley Speed 8 beat Audi at Le Mans?
As daan, I'll provide two possible replies, both correct, but none has to do with classes. "Beating" means "1st place overall, whatever class isn't relevant".
Reply 1 - YES. There were Audi R8 cars racing when Bentley won Le Mans.
Reply 2 - NO. All Audi R8 cars presente that year were run by privateers (Stefan Johansson, Team Goh) , and Joest Racing (usually running the works Audi team), was running the ... Bentleys. Audi Sport didn't show up, hence, it wasn't beaten.