Bottom line is that very few yeshivos and camps have a formal hechsher. Does the Mir kitchen have one? Did it always?
There is a knowledgable person in charge of the kashrus. That does not mean that there is a outside hechsher.
AFAIK At least at two points in the last ten years, when issues where brought up to the attention of the RY, significant changes were made in the kashrus system. At some point, the EC came and did a reveiw of the whole system.
They have at least 4 paid mashgichim who don't have any other responsibilities.