I am not in the fire Roger chorus (not for this anyway) however, he does have some blame in this area if not this incident.
He has constructed a system of procedures and policies with no meaningful checks and balances when it comes to Player Conduct. It is inconsistent and a virtual closed loop. Its produces neither certainty nor any degree of trust that it was complete. Its seems mostly arbitrary. Even of-field conduct gets reviewed by arbitrators chosen jointly by the League and the Players. Player Conduct is reviewed by the prosecuting attorney, who is also the judge.
Take for instance, the current stance on McDonald for the 49ers. They are waiting for the court case. But in other circumstances, he has acted prior (see Aldon Smith or Rothliesberger). Does anyone know how that decision is made? It doesn't seem consistent from case to case.
Now in the Rice situation, we know the NFL is willing to act when it is not in possession of all available information. But its investigation not only was incomplete, it had ended. And there has been no explanation how such an oversight occurred except that they stopped asking.
He has made himself a one man gang on this issue, and is mucking it up. That is not effective administration.