There are also photos of this guy hovering around Bill Clinton when Hillary is elsewhere.
He might be retired SS working privately based on some especially friendly relationship, might have a fitness waiver, special med background, etc.
An MD, especially a specialist, would have been ID’d by now. A SS guy or some other government employee could expect to remain somewhat anonymous.
The Clinton’s have had a SS detail for decades. I’m sure they’ve slipped in some of their own people onto the government payroll.