Not sure if they are still doing this or not, we last did it about a year ago. But at least back then, and I'd done it many times before that, if you stayed at the GCH, and they specified it was only that hotel, you could get in even before the half hour early opening. You had to show up at the GCH DCA entrance about an hour before opening and ask for the special tour of DCA. The gate attendants knew what you're talking about, but the front desk knew nothing about it, I'd asked there before. There was someone who showed up to do the tour, it was free, and only the people who showed up and asked specifically for the tour would go. I saw loads of other hotel guests show up to that entrance, and they would be directed to go to the front entrance, or to wait until park opening.
They would take you into DCA and give a mini-tour of the Grizzly River area, then walk into Condor Flats and explain that area, and then they would take you on Soarin' all by yourselves. One time our group consisted of my husband, myself, and our 2 friends. We were the only ones on the ride and got to sit wherever we wanted. When we got off the ride, the line was forming from the people who were came in the half hour early.
While waiting to enter into DCA through that entrance one time, there was a group that wanted to get into the park and said they were staying at the hotel. If they did not have absolute proof that they were staying there, with their hotel key or their charge slip, they wouldn't let them through, no matter how much this group protested. This was in the morning. I've entered through that entrance many times after lunch when I've not been a hotel guest. The gate attendants told me that after lunch they didn't care as much, it was in the morning hours that they cared.