Yes, fruit flies can be gut loaded. That is how the "color enhancer" thing works in the fruit fly medium. It is somewhat easier than crickets, as crix don't eat as much once they have plenty of fish food, while fruit flies eat constantly in their short lifecycle. Crickets are very expensive though, and its not very practical unless you've got a lot of time to breed them yourself, or the food bill will be huge. I know a lady with a ton of herps that spends nearly a $100 a month to feed her collection. Not something I would want to do. Plus, crickets smell a lot WORSE in my experience than the tons of cultures I got. I never use potato flakes either, and I discard my cultures quick when they start going bad.
You could try lobster roaches. However, roaches are somewhat hardier than crickets are, and they could survive in the terrarium until adult size. Not something I'd want to deal with.
If I were you, I'd experiment with different mediums, containers, etc. to get fruit flies "down to pat." I spent a month just perfecting my culturing ability before I got my dart frogs and mantellas. You might want to house your fruit fly cultures in a 10 gallon fish tank with a small light and a heat pad to keep them healthy, in your basement. Or simply put, a self contained enclosure containing the cultures, a "food cabinet." I keep some of the cultures beginning to smell down stairs in the basement, while the fresher cultures are upstairs.
And, do you have any cultures of flour beetles? They are so easy to culture, and are good for times when your cultures go bad, or just to add some fat to baby froglets.
