Personally speaking I've never had discus take another fish over the wiggler type stage, kinda like mosquito larva size and appearance. I've seen reports of them eating neons/cardinal tetras and smaller fish like that but don't have experience with that myself. I think one of the problems with doing this, is despite growing them yourself they are a freshwater fish and could carry parasites into the discus (Though one of the more experienced members can shed more light on this as I don't know if the parasites start from day 1 fry stage or what) that could eventually effect the discus. This is the reason so many people use seafood in their food mixes instead of freshwater fish which would be much cheaper.
While it would be a dream food factory given production rates I'd personally shy from it and stick to multiple other options out there for a protein rich diet like a beefheart mix or FDBW. Maybe it is being overly paranoid but it could save you headaches later.