Answer

You are not benefiting from Sabbath desecration, because it is his own decision to do it on the Sabbath. He could also have done it on a weekday. You may even employ him in an indirect/inclusive way. All the more so since he probably does not believe in Jewish law, and therefore his transgressions are not considered transgressions. And certainly this is no more than inadvertent violation. Therefore there is no prohibition of benefiting from an act done on the Sabbath for others (though not for the person who performed it himself) after Saturday night.