The consensus seems to be that frogs don't care for pelleted food, in general. However, I've read of it occuring in situations where the bottom of the tank or bowl is either mostly empty, or entirely empty.
Frogs prefer frozen (thawed) or live, wormy foods. They have fairly odd eyesight, in that they can see things that wiggle about 1-2 inches away from their little faces, but if something falls on their head, they're oblivious. They also have a very good sense of smell. A little bit of bloodworm juice in the water and they come dashing to the front of the tank (where I feed), and fall into 'hunting mode'.
If you want to pellet train your frogs, I think that you'd need to start by making sure that the food itself is sitting in a fairly open place, or take a pair of tweezers and wave it in front of them. That's in my opinion... I tried feeding my frogs HBH Frog and Tadpole bites 3 times just last week, and they didn't notice them at all, floated right past 'em. However, they would definately be the most appropriate pellet out there.
They're really easy care. I totally dig having them in my tank. I feed mine thawed bloodworms, mostly. If I could just get them to recognize the pellets as food, I'd also be feeding them that as well.
If they're juvies, feed them daily. If they're adults, every other day is fine (but daily is still good). Juvies are usually under an inch in length, from snout to rump.
Did you already check out the standard 'flippers and fins' and 'frogland' websites?