Glad to know so far no one else has heard these horror stories. I was at least partially more concerned because the tree frogs are too big to be interested in the springtails, so I know their population is going to surge.

So long as no one else has had critters chewed on by springtails, I'll probably toss them into the substrate in the next day or so. I guess if they won't eat the roots on my live plants, not much risk of them eating my frogs -- though the idea of brumation in the substrate with the springtails is still faintly concerning. I don't really know how deeply the frogs sleep.