But he has yet to be a hearing officer in any instance. Nor has he overturned any decision made by the appointed hearing officer, even at moments where they have disagreed with Goodell (and there's multiple instances of a player winning an appeal to some degree).
Until there is any proof that Goodell is changing, checking, or sitting in on an appeal, he is not involved. The fact that he can be an appeals officer is likely only a fail safe in case of an extreme situation (where the other two appointed officers are unable to make it to the appeal) or some crazy situation of blatant abuse by one Shell or Cotrell.