They may be referred to outside sources by the military, but the general principle of continuity of care requires that they be part of the military health system, that their care be quarterbacked. There have been some tragic, tragic circumstances, in cases that have led even to deaths, where care was sought, unbeknownst to the armed forces, outside, and then, not knowing what their circumstances were, they were deemed fit to deploy to operations.
On April 8th, 2014. See this statement in context.