That is a little known fact. My dad was a retired doctor. He was a hospital commander during the latter part of his 33 years in the Air Force. Finished up commanding Wilford Hall at Lackland as a one star. He got a call from Washington during the build up to Desert Storm. He was in his seventies but they were planning to bring him back in to coordinate the call up and drafting of doctors.
As a serving member of a local draft board; there are actually two separate drafts possible. The general manpower draft; perhaps the one we are all most familiar with. And the Health care draft; the SSS maintains a list of healthcare specialties and can draft as needed. Interestingly, the upper age limit for this effort is much higher than the general draft. Should you be say a 20yr old RN, you would actually be a ‘dual registrant’ subject to both drafts.