Dor, I just saw the video (I presume that you are referring to Dr. Robert Jeffress). . He prayed to “the Gd of Abraham, Isaac and Jacob”. At the very end he referred to that man as the “Prince of peace” and “our (a presume he meant Xtians) lord”. “Lord” can simply mean “leader”. If they want to consider him their rebbe I have no objection. BTW, another Chabad rabbi was right there with him and spoke right after him.
How does sitting at an event not in a church (which is ordinarily a problem of marit ayin that one is praying there unless it is obvious that one is not) imply agreement? Jeffress also praised Netanyahu and Trump. Does sitting there imply endorsement of either?