When you use your (US) Visa, you're paying with dollars. Your obligation to repay is with dollars. And your statement will be in dollars.
And maybe some day in the future the federal government will, like those state governments, decree by FIAT that gold is legal tender. And then it will be.
Regarding Visa, you are not paying with dollars. You are paying with credit - a promissory note, if you will. So credit is money too. Hmm.
So is gold money in those states that accept it? I didn't get your answer on that (and I suspect I might not ever get it).