It does not say specifically. The way I read it, if they cover a procedure for a reason that isn't gender related they have to cover it for a gender related reason too. Oregon doesn't spell out what has to be covered, only that the coverage cannot discriminate against gender diagnoses or deny based on gender.
This is new stuff and I am no attorney, but I would suggest two areas that might have a chance on appeal, based on this bulletin: as corrective surgery or as reconstructive surgery. One would have to show that the medically necessary service is indeed covered for at least one other condition under the same plan.
So lets say a ciswoman is born with a birth defect that caused the vagina never to form but they are normally female in every other way. If the plan would cover construction of a neovagina for that girl, then they would have to cover it for a transwoman with a medically necessity for the same service.
Or lets say a cisman had his penis destroyed by cancer and it had to be removed. If the plan would cover reconstructive surgery to create a new penis for the man, then they would have to cover it for a transman with a medical necessity for the same service.
In either case, if the plan was written to not cover that medical service for anyone regardless of the diagnosis or patient situation, then it wouldn't be covered as treatment for GD either.
This is my personal opinion and does not represent the opinions of this site, or my employer, or any other person.