@Cooperd0g is right. USMC is who bottom lines it.
The DH may be concerned about the hit the clinic will take with available appointments and access to care. Perhaps that is what he is blaming on DHA stuff.
Ultimately the DH will just have to deal with effect on clinic as you don't officially report to him or her. That being said, 85 days of terminal leave is very large for a junior officer so I can understand the concern. Someone should have recommended that you spread out your leave. Even 10+ year staff at hospital aren't allowed to take that much, but then again they are under direct chain of command. Remember that earning leave is a right, when/how you use it is a privilege granted by CO.
So ultimately you can likely take whatever your USMC chain of command will give you. I just wouldn't dog on the DH too much for being concerned about the hit on the clinic. Although, if they are a good DH utilizing green side providers in the template then they would not be reliant on you to maintain access to care....they should just be happy you can provide your additional services while you are there.
Good luck on the transition!