Okay, on July 5, after we vacated our room, we walked our bags to our car parked in the self parking lot across the street. When we came back in through the gate to spend the afternoon at the parks, we used our room key to open the gate and a family tried to walk in behind us. The guard asked them for their room keys and they showed him one from PPH and he said "this entrance is only for guests of this hotel. You need to go back across the street and follow the signs towards the entrance at Downtown Disney ." And he pointed on the general direction. They tried to argue, but the guard held firm with a "sorry, that's the rule."
There is an actual door on the sidewalk with a key reader. Only GCH keys will open the door and there is always a guard standing there as well. There is also a sign indicating that the entrance is only for registered guests of the Grand Californian.