DY: “He only differentiates in the sense that if there’s no supervision, it’s not even a shaila, but is explicitly machmir even when there is no chashash that he would add something unkosher”
No. He writes that when there is supervision, there is no issue of Ma’achalim Assurim. the only remaining concern would be Chasnus, and on that he concurrs with the Tiferes l’Moshe that Chasnus does not apply to a Mechalel Shabbos.