springtails are pretty small, I don't know how big chorus frogs are but if they're the right size, go for it. You might need to dust the feeders though.

As far as mixing,"chorus frog" is a name for a lot of different species, including spring peepers. I wouldn't mix them if they're different though, just to be on the safe side. Different species have different levels of toxins in their skin and over time sometimes one can harm another.