I used to work in luxury hospitality, as everything from receptionist to duty management, as a student. Believe me when I say there is every chance you'll be spotted. Staff at posh hotels have some kind of a sixth sense for imposters - it's not as though they don't get to practise on a daily basis.
Be prepared to be confronted by a snobbish duty manager or security guard who, depending on current level of outrageous complaints, may or may not experience a sadistic sense of pleasure at humiliating you in front of everybody - especially that gorgeous lifeguard.
Floggingmolly, on some booking sites (notably lastminute.com IIRC) booking a 'secret hotel' basically means that you reserve a room at an establishment without knowing which hotel it is. Room rates are usually heavily discounted. It's a way for hotels to flog off the rooms they wouldn't otherwise be able to sell without lowering their official rates too far. The downside is you'll usually get the worst rooms in the house for it.
You can play the system quite beautifully, though: with some internet research you can often find out which hotel it is by comparing the description with hotels in the area. You then buy a room at a ridiculously low rate and, once you have confirmation, ring up and purchase an upgrade to the next best room category (for which you pay yourself).
Usually this will get you a nice room at the hotel of your choice at a price which may well be below the standard rate for the most miserable broom cabinet in the house.