I don't have any hard and fast data, but I think medical students have been fairly successful in applying to business school. There were three in my class at Duke. The admissions staff would be looking for the same things it looks for in other applicants: ability to handle MBA-level work, clear short and long-term goals, ability to "add" something to the class, etc. When seeking individuals to write your LORs, identify those who can discuss your accomplishments and strengths and who also have an understanding of how an MBA will help you to achieve your professional goals.