I agree with bond-007. It would be a farce not to recognise a divorce lawfully granted in the USA. Does that mean he is not married in the USA and still Married here? Pure madness.
I happen to have a US divorce, I live in the UK. My ex was born in California but she lived all her life in Oregon. Now the courts in California would not deal with any divorce request as neither party was resident there. So I had to use the Oregon courts. Now you are saying that because someone was born in a different state the divorce is not valid. That is madness.
I would advise the OP to go to Las Vegas and get married there. They have will have no problems recognising your divorce. Ireland will have no choice but to accept the marriage afterwards.