I'm the opposite. RB is the most instinctive position in all of football so "practice time" is least necessary at that position more than any other. If his hammy is tight AT ALL this time of year (6 full weeks still before game 1), I don't give a flying crap about him practicing now and would rather him sit out another few days.
RB is also the most oft-injured position in football. The less hits he takes before they matter the better as well. We all know the dude can take (and dish out) punishment. No need to "show off" now.
I hear what you are saying and I agree that there is no reason to rush him out there if the hammy is less than 100%. My only point is that if he is out there, I assume that the hamstring is not that big of a concern.