AidemAmok I have the same questions and nobody has been able to answer it so far, mostly because 1. Most people get their insurance post (legal) transition so there's no issue, or 2. They don't have insurance at all.
The best answer I've gotten is that it's case by case depending on your insurance. "Legally" they're not allowed to discriminate but companies break the law all the time with no repercussions, so dunno.