I have been "on the Rock" a couple of times just to visit and gawk.
Asking about food and hot water at any third world accommodation is highly dependent upon if you're asking about yesterday, today, or tomorrow. Things can be transitory, changeable and a bit unpredictable. Roatan has become so annoyingly civilized that visitors ask/complain about Internet access. Now you're asking about a citadel perched on a rock a few miles offshore of the backwater last-stop-on-the-trolley, Guanaja. I think you can buy Diet Coke on the population center of Bonacca Key most days of the month, but then you have to motor over there and buy it when the Walmart is open.
Such is the nature of adventure travel, and a trip to Dunbar Rock fits into that adventure travel niche with little argument. In these days of homogenized travel, there isn't much left in the Caribbean that lies in that category.
Go, have fun, be a person who can say, "I remember when....", no less that when we old people reminisce about the primitive nature of Grand Cayman in 1970. Some people go to GC today and start feeling all Anthony Bourdain, "exploring " in their rental car and assumably a pith helmet. Bless ther heads.
In re nitrox. I've done quite a bit of private liveaboard diving all around Guanaja. The expected resort-based dive schedule is 3x a day. It is quite likely spread out thru the day, not even two tank boat dives. Whatever. The local reef structure and the critters you come to see mathematically add up to very shallow average dive profiles.
With the above in mind, there is no predictable need for nitrox. If you "want" or "desire" something that may not be a local standard requirement, much as Diet Coke, you might be SOL.
Be flexible, go have an adventure.
