i was also defered fromt he army on medical grounds; i even tryied joining the TA but i was still defered until march 2010.
i decided to try and apply for the RAF i was susscefully and im going in febuary 15th, so the answer to your question is yes you can and you've also got more chance of getting in, well i did!
if anything theres no harm in trying.
I am in the same boat as you got deferred for the british army till sep 2013 because of minor eczema on my medical records. I am going to apply for the raf and was looking for advice before i start my application , could you tell me if i should liar on my application where it ask if i have had a application for the armed forces before, what did you put down on your application i need advice i want to get in bad. Respond asap thank you.