I was told that you do have to tell them (I feel the same way, having to pay an extra $25 per night for ours ugh), apparently they would not receive a room key with charging privelages on it also, not be allowed early entry to the parks also if they try to use any hotel facilties they "may" have to show that they are staying at the hotel. When it came down to it, we decided just to pay for the 3rd adult, I wanted to have fun and not worry the whole time about "sneaking" around =/