Assuming they are morning EMH the park is open 2 hrs before normal opening time (usually 10.00) so it usually means you can get in at 8.00. And yes you can use them staying in DCR.
Not all rides are open but its usually Space Mountain, Buzz, Orbitron in Discoveryland and Carrousel, Dumbo, Peter Pan, Teacups, Snow White or Pinichio in Fantasyland.
Also the castle is open and a few shops and restaurants
If the park is busy it is definitely worth getting up early for. We rode Pater Pan 4 times in a row with no queue whereas later in the day the queue was for 90 mins.
We had managed to do PP (x4), Dumbo (x2), Carrousel(x2), Teacups, Pinochio and Buzz by about 9.00.
One morning we then queued by the rope leading to Adventure land from Fantasyland and were more or less first on POTC when the park opened properly. Another morning we queued to get into Frontierland and headed for BTM ahead of the crowds.
We found getting in at 8.00 was even better than by 9.00 as by then it was getting busier. We forgot about breakfast until after having done several rides and then grabbed something from Cablecar shop.
