What exactly is the concern here?
Quite honestly it seems that you see a soldier running and you're like "OOOOH, I'm gonna tell on you!!"
So long as he is following his own profile and still conducting the walk to standard, I do not see a problem.
Granted, I SUPPOSE you could speak to the 1SG or the commander about your "concerns" and actions can be initiated for him to be reevaluated by a COMPOTENT MEDICAL AUTHORITY or malingering charges be brought against him. I say this because you stated "Over the last two years he has successfully rehabilitated..."