I haven't been for two years so maybe this has changed but when we stayed at the GCH each person in our group (myself, husband and two kiddos) each received a hotel key, I even think it had our name on it. I believe we had to show each key along with our tickets to get in early.
As others have said, you just show your key cards. One nice thing to consider is that your room key is good for EMH on both your first day at the hotel and your last day. On the first day, you would have to plan things such that you can "check in" at the hotel prior to the start of EMH. They will issue all of your room keys at that time. But they won't be active until a room is available and assigned to you. The bell hops will store your luggage. And on the last day, they will also store your luggage so you can enjoy a full day in the parks without worrying about going back to check out.
Dreams Unlimited Travel is committed to providing you with the very best vacation planning experience possible. Our Vacation Planners are experts and will share their honest advice to help you have a magical vacation.