2 things:
(1) Tricare covers family members too. Children of servicemembers, and occasionally spouses, get trans-related treatment covered under military insurance.
(2) Military insurance covers all manner of conditions that are medically disqualifying. You'll find that diabetes is also covered - but it, like being trans, is an absolute disqualifier. The military provides virtually any medically necessary treatment to people who have already joined before being diagnosed with a condition- that doesn't mean they'll let you join with that condition. They provide physical therapy to amputees, too, before they kick them out...