I think that you need to contact individual schools for this one. Different schools have different deferral policies, some of which are idiosyncratic. You just need to ask around.
Many schools (other than "top tier" schools) tend to be leery of granting deferrals. Why? Because in the past, some students who have requested referrals have done so in order to keep the school as a 'back-up' school while applying again for medical school the following year. If they do get in at the school of their choice, they drop the school they have deferred at and matriculate at the other school. Obviously, this makes the school at which the applicant deferred at pretty jaded.
This scheme sounds pretty opportunistic and sleazy to me. I think most schools are pretty open about deferrals as long as you are very honest about it from the beginning and seem to have a coherent plan of action concerning what you are going to do the year that you defer.
Hope this helped. Good luck.
xena
