Allan,
No, of course not. NASCAR cannot take all the credit for the FE engine development and creation. The engine saw corporate duty in trucks and cars throughout the 1960s. While I am no FE expert, in fact I don't really like the motors at all to be honest, lots of information on how the FE performed, could be made to perform, and held up came from street use in trucks and cars. Bear in mind the FE engine used was not the special built SOHC 427 motor that was subsequently outlawed in NASCAR. That motor was purpose built as Mike indicates and is not an FE motor as what we think of in NASCAR and MKIIs. I'm sure there are guys here that can give you the entire history of the FE and cover my mistakes, but don't confuse the 427 SOHC NASCAR Galaxie motor that was outlawed with 352/360/390/427/428 FE motors that ran in stuff all over the place.
Now the basis for the new GT motor hasn't been raced much at all except in 03-04 Cobra's using the 4.6L blown block, and the 99-04 Lightning in 5.4L iron blocks with 2V heads. And, what racing is done with them happens a quarter mile at a go since not many of these see real road course duty.
So, I don't think the Viper is the only car with an engine rooted in truck and car duty. The modern day GT definitely has its roots there for sure as do vintage NASCAR and MKIIs. If I am not mistaken the FE engine started life as a 332 inch V8 in trucks, but I do not know what year. Eventually it made it to 428 inches with a 4.13" bore x 3.98" stroke.
R
Ron