“When a kiruv person helps someone become frum, they often do not know the lineage or familial background of the non-Orthodox person. ”
Nonsense. Kiruv professionals almost always find out if the person has a non-Jewish mother, especially if the person starts getting serious. The situation you a insinuating where someone is completely mekereved, and then finds out they’re goyishe after the point of becoming fully frum has probably never occurred in the history of all mankind.