The main staple for your dart frogs should be fruit flies. Pin heads are fine but you should think on changing over to fruit flies. There are some threads that address the issues with darts and Exo-Terrra enclosures and how to seal them up to reduce the amount of flies lost through the screen and seals on the door/doors.

One of the things to be noted here is that the media for culturing fruit flies contains some of the needed nutrition required by the frogs.

Can dart frogs survive on pin heads dusted with vitamins and calcium? Not sure the long term answer to that.