Actually though, and you probably know this, the key cards will tell you what level of room a person is in if you know what you are looking for.
This was actually on the Regatta, another poster mentioned it and I recently checked it out less than 2 weeks ago. Yes, there is no lock or any sign of any description saying restricted to Concierge and above. So, if you didn't know you weren't supposed to be there or just wanted to go out there it's completely available to everyone. I don't know about any of the other R ships. I'll check Nautica in August. Although truth be known I really don't care much about going out there even when I have access. Only time I took full advantage of it was in Venice on the Riviera during the sail out. My wife and I were the only ones out there. That was pretty cool.