For an offence of fraud it is not likely that your boyfriend would have been granted a visa. The U.S.A. insists on passenger lists prior to take off now I do not know how thoroughly these lists are checked for criminal records rather than just 'undesirable individuals' but my experience of American immigration is that it is very tough. I do not think I would just take a chance but that is up to your boyfriend he runs the risk of being detained by immigration and sent home straight away. Good luck.