Works as with any other graduate or professional school, some loans can defer just payments, others can defer both interest and payments, and some can defer interest as long as you make a minimum payment during school.
I know someone who applied to work in Kenya for a year at the same time as applying to medical school. By the time she got accepted to med school she knew she wanted to go to Kenya first and they had no problems with that what so ever!
I deferred one year to KCUMB because my husband did not have a job in KC the summer before school started. We have two small kids and were moving to KC from out of state. It was not a big deal. I just called the school and wrote a letter and it was granted. They were very understanding and just asked that I kept them up to date on our move. I had already paid both deposits and they transferred them for next year.