The rules at OATS are there to be broken! I am currently at OATS, and lived in the glorious accommodation for two months before getting a house with fellow self-sponsored guys.
Many a time have my sponsored class-mates had friends up who have spent the evening in their rooms with them. There is also the huge TV room where many people have been known to crash (although only at the w/ends when the cleaners aren't around). The 'no people in your room after 11pm' is a load of cr*p.
The accommodation in general isn't too bad. Langford is the nicest block, whilst Cherwell is right by the main building and has a fire-alarm test every morning around 7am! The rooms are a decent-enough size, and you share a shower, toilet and bath with about 6/8 other people. Having never been to Uni, I have nothing to compare it with, but as long as you bring enough stuff, you can make your room pretty homely.
Just don't forget the ear-plugs to block out the noise from the numerous orgies going on down the corridor!