Correct me if I'm wrong, but I believe some states already allow marriages which some other states will not recognize, period. While I would doubt that a 40-year-old man who legally married a 14-year-old girl would be prosecuted for statutory rape if he moved to a state that didn't recognize the marriage, that doesn't mean the state would accept the marriage.
Yep, that would be true.
That being said, I don't think the USSC would see it that way since it has already laid the groundwork to consider sexual orientation a sphere for it to work its Equap Protection analysis.
That is, it will not find a compelling state interest that would validate, in its judgment, discriminating against homosexuals in this case.