I think you are mistaking the term Crypto-Jew with a shabbos goy.

A crypto Jew is a Jew pretending to be Muslim, Christian, etc.. And yes they need that so that that non Jews do not suspect them or see the extent of their control. Makes no difference where Christianity came from regarding that.

A shabbos goy on the other hand, is someone like Mao and Stalin. They are not Jewish, they may act Jewish, believe the ideals of the Talmud, etc.. but they are still not Jewish, they simply have understood Jewish power and decided to cuck themselves to it.