I've raised silkworms in the past for other herps. The only drawback to them is that they take a lot of care, and they don't move very much. The frogs may not see them as food, since their prey has to be moving for them to notice it. Now, I've never fed them to my frogs, only geckos and dwarf monitors.
I use to raise these when I kept chameleons and thought they were rather easy to keep. My parents have a Mulberry tree in their backyard. So whenever I visited them I would grab some leaves. I think they were the easist thing to care for. I had them in very shallow tupperware, filled with Mulberry leaves and thats it! They wouldn't try to leave the containers (I didn't have alid on there at all!), and were funny yo watch each and move around. They don't move a whole lot, but I think enough that the frogs would attempt to eat them. Chameleons (actually most lizards) hunt by using movement to locate prey... so I think they move enough for the frog to notice them. I would think it would be best to add a few first, as if the fros don't eat them they will settle in and not move as much... so they could sit in the tank for awhile (but this wouldn't hurt anything anyway). I have always wanted to try it... but they grow so fast that most darts won't take them. If you have some Phyllobates or Epipedobates I am sure they would take care of any of the bigger ones . Well good luck with them.