I see another problem with that though. How strong are the mandibles on the cockroach? People who try to use them in an enviroment with frogs/snakes usually end up with nasty bites on their animal. It works fine until they get hungry, theres no waste to eat, so they eat the next organic matter.

It sounds far fetched, but we had a problem with crickets biting animals last year, and it may be the same with cockroaches if their bite is just as strong.