Well, all I can comment here, is feeding scorpions should be fine, especially if they are frozen. Remove the stinger and venom duct (aka their tail) to be safe. Scorpions are totally edible. Many years ago I had a tegu lizard, and 'rehomed' a group of emperor scorpions a friend no longer wanted to her, she had a land-lobster feast!
I should mention though that feeding any wild-caught invertebrate (or vertebrate for that matter lol) has the potential to transmit parasites.
As for what species they eat in the wild...just look what species are found in their range. Are you asking cause you live in an area you can collect them? To be safe, avoid species with thick tails...general rule of thumb with scorpions...thick tail and stinger w/thin claws = dangerously venomous. Large pinchers/small stinger = not dangerous. Just a generalization.