If I recall correctly there was a similar discussion on Grado drivers sometime ago (I tried searching for the thread to no avail). If my memory serves correct it was in relation to the Grado facilty tour back in 07. The identical question was put forth "does Grado produce drivers in house" as well as "are the same drivers used".
According to what one member described (beleive it was Immtbiker) he saw first hand the actual tooling and machine in action producing the drivers. At the time, Zanth also was told by John that each driver was produced in house.
As far as "doping" goes or "tuning" if you like there has always been some speculation regarding the black putty placed behind the drivers on such models ranging from the RS-2 and up. According to another source at Grado (John Chapais), the coil (relating to how it was wound) tuning also played a large part in each models sound sig.
If you refer to some of these older pics from Grados site
http://gradolabs.com/page_tour.php , there was also discussion on wether the drivers laying in the plastic trays were merely Chinese produced cheapies. It was however put to rest that as mentioned earlier these drivers were in fact all created in house.
I suppose you could say that in a nutshell each driver may begin its life as a clone of the one next to it, but depending on the model its being housed in (or intended for) Grado applies different recipes (putty / coil tensions) to allow for the sonic differences.