I have not been on the Dream yet but the pictures I have seen give me a different impression of what is behind the locked gate. I actually believe that
there are staterooms behind that gate, at least on deck 12. Look at the picture below:
First, notice the stateroom door. Then, look at the wood paneling on the left of the picture. You can see the reflection of the gate in the wood. There are definitely rooms behind the gate.
Edit: See the very beginning of this video:
http://www.youtube.com/watch?v=xnJQq2p4JZI&feature=watch_response_rev
for an idea of how to get to the lounge.