No, there was a posting years ago by Simon from Prodrive where he mentioned that they buy from Subaru these cars, because they are lighter and cheaper, more suitable.
There was never any mention of Subaru restricting anything about selling them, that wouldn't make sense anyway.
There is nothing theoretical about buying this car.
The ABS was not some kind of feature. ABS and DCCD were incompatible, upto when the Sti started in the US. So they had 2 options: no ABS with DCCD or viscous with Sports ABS.
With the 04 , they started to have the technology to make both work, so they offered both together in Sti and spec C.