I'm sure some guy, somewhere may have figured out the scrub prior to JS7, but James is rightly credited as the pioneer of the technique ...
I've been paying attention to US pro motocross since the early '80s ... still mourning the loss of 'Motocross' magazine. Not MXA, but it's sister publication, that was dedicated to the riders and lifestyle of motocross racing. I believe it stopped publication in the 1990's ...
I digress ... Anyway ...
Prior to JS7 entering the pro ranks in the 2002-03 timeframe, the scrub was not a common technique in pro MX. I don't know how or when JS7 figured out how to scrub, but him doing it in the pro ranks was a pioneering move on his part. Once he showed it, people started talking about it, and all the other pros figured out how to do it.
All else aside, that can't be taken away from him.
Just saying ...