I would be very suprised if it was common practice for OASC (or whatever it is called these days) to look at candidates civilian medical records. The organisation required to gather the documents of an entire selection intake would be well beyond anything I've seen from either the NHS or RAF Medical branch.
I suppose they may ask for a look at them if the medical throws up anything contentious, but I seem to recall that you have the right to be consulted if they decide to do that.
Provided you are not a wheezy kid and have no reason to believe you will become one, my advice would be to keep schtum. It worked for me, and after 15 years of flying if they want to kick me out for lack of integrity they are welcome to try (it would please Mrs Fufkin no end!!)
Good luck
Arty