Does Progenitor Mimic create copies of itself even when it isn't a creature?
Yes, it does. When a card says "this creature", is still refers to itself even if it is no longer a creature, so the ability still triggers and resolves.

According to rule 201.5,


  If an ability of an object uses a phrase such as "this [something]" to identify an object, where [something] is a characteristic, it is referring to that particular object, even if it isn't the appropriate characteristic at the time.