I’ve searched high and low for a quick reference to reporting such and can’t find it. Your situation demonstrates that so many focus on the same sex aspect of BSA’s policies, myself included.
So I contacted my local Scout office and was told that even in your situation, to contact the District Executive or go to the Council Executive immediately and report it.
I’ve been searching for the National policy on line, but can’t find it. I’m either using the wrong search terms or it’s not out there. I get lots of pro-homo links though.
I did some searching when a local politician who was publicly gay listed scoutmaster on his resume.
So far as I can tell, nothing on the scout leadership form explicitly asks the question about sexuality. It does require a signature affirming you will follow the policies, and the policies is no gays, but if you are willing to lie, and nobody reports you, the BSA appears to take a “don’t ask, don’t tell” approach.