Health,
The Aruch Hashulchan is only matir if it’s an employee, and one of the factors is that a Jew will likely aid in the cooking, which certainly can’t be said in this case.
I don’t know who your rov is or what his sources might be; the Shmiras Shabbos K’hilchoso clearly includes an elictric hot plate in the category of “aish”, and the IG”M holds that even a microwave can produce bishul D’oraiso, so even were we to find a source that a covered element is not aish, according to the IG”M it would still be bishul D’oraiso.