Zophobas morio are perfectly safe to feed; though they do have stronger mandibles than mealworms and care should be taken not to overwhelm the animal with them or leave them unattended without a means of escape (just as you would for crickets). What species are you feeding?

As for the fruit juice: Avoid high citrus fruits, or anying with added sugars (or High-Fructose Corn Syrup). Most herps have some difficulty metabolizing sucrose. I've always been a fan of POM wonderful Pomegranate mixed fruit juices for reptiles that tolerate fruit well. Makes for a nice mix in with oral medications as well.

BUT - in reality. Your frog is probably a strict insectivore, and it would be best to leave the bugs to eat the fruits and gutload incrediants, leaving the frog to reap the benefits after they have gotten a start on the digestion. I'd just stick with what you are doing, gutload the bugs beforehand and dust the insects just before feeding. = )