I recently heard that using instant pie filling as a filling for cake layers is a great non-refrigerated option....is this true?
Do you meant instant PUDDING & Pie filling?
If you make it with milk, it has to be refrigerated.
If you make a paste of it with hot water and mix that into whipped Bettercreme, then, no, it doesn't have to be refrigerated.
If you mean the cans of fruit fillings used for pies, then yes, they make great fillings (as long as they're not too runny) that don't require refrigeration.