Yes, I agree that all feeder fish will likely cause problems. "Other safer possibilities" would include live earthworms etc.
I had a problem with crickets used to kill them now I put a plastic containner out in the back against my wall and catch about 10 to 20 crickets..... I feed them to my oscars and turtle...I'm raising cons and guppies but give them like once every other week....
unless you raise your own crickets you run the big risk of pesticides, insectisides, and herbersides etc etc in the soil.. which will eventually kill your fish..
That's why I buy crickets that were raised just for feeding.