My teenage son desperately wants to live with me in the States, and not with my “ex”, his mother, in Israel. Is this still possible, if both my “ex” and our son are Jewish, but I am not Jewish and his mother objects vehemently ?

Yes, subject to a positive recommendation from a court appointed expert (clinical psychologist) who would most probably be appointed to make a report and recommendations, should you bring legal action at the family court in Israel. The court can also give a decision allowing trial/temporary relocation, which includes a mechanism for follow-up before a final judgment is made.
In proceedings initiated in 2017, in which our law office represented a non-Jewish father in Australasia, the Israeli family court authorized temporary relocation of a teenager ,into the father’s temporary custody overseas, by consent, in January 2018, despite initial strong objections from the mother, who observes an Orthodox Jewish lifestyle. The breakthrough came after a court appointed expert filed a report overwhelmingly recommending a trial move. He was satisfied that there was no parental incitement and that the move expressed the minor’s true wishes, which he said, should be the determining factor, given the minor’s chronological age and emotional maturity.