I had purchased them as a kid. Got a few to hatch and thought it was too difficult at the time to keep up with their water changes and they got stinky pretty quick. Now we raise millions every day to feed our fish and invertebrates. you never know how things will turn out.
About the original scud question, there are warm water and cold water species. The warm water ones, e.g., Hyalella sp. are not difficult to raise, but that is on a small scale, like thousands. We don't waste our time on trying to rear the coldwater species like Gammarus sp. due to water usage, diet and cannibalism. When we test Gammarus we will use field collected animals. I would think that it would take a considerable effort to try to rear them in large scale production.