Rusty' moss is fine aslong as its not green moss, spaghnum is fine because if soaks up more and thus pats down well, as well as having longer and thicker strands less likely to get eaten than cheap green moss. I've had impactions from cheap green moss, which will pass as doing what you said but no cases of impaction from sphagnum. So I wouldn't worry about it I also consider crickets to be a good source of food because they can be gut loaded easily and are easily coated in supplements, then again worms are healthier and will not feed on frogs like crickets will.