Well, i think it's because he said he breeds them. So from a
practical sense i can see why he would like to know if it's okay. It would be a natural way of culling out the "unwanted" babies that would otherwise not survive to maturity or would have been eaten anyways in the wild. I know it may sound cruel, but it is a natural process and we are trying to keep these animals in an unnatural setting.
As long as there are no toxins in the tadpoles or froglets, it would be a healthy and free supply of live food from a safe and controlled (pesticide and disease free) environment. If I were you I would do some more indepth research to make sure there are no natural toxins though. I'm sure there are plenty of scientific papers available on university web sites about it. Like Jen said, it's not worth risking your turtle's health unless you know for sure that they are safe to eat.