yup..
crayfish are "detrivours" and usually only consume dead/rotting things.. a good sinking pellet (like catfish food) is an appropriate feed..i don't see baby crayfish being able to survive very long in a flood and drain growbed, unless you have a void (no media) in the bottom of the bed and don't flood all the way..
if you're only doing DWC troughs, you'll need some filtration, some young may get trapped in the filters but they would be fine until they outgrow the space
and yeah, the fish will eat them if they can fit them in their mouths