Been feeding Earthworms for years.My take on this is all animals have parasites including ourselves,however terrestrial creatures such as worms,crickets etc cannot live in an aquatic environment and neither can their parasites so they wont cross infect.So long as the area where you collect your worms from is free from man made pesticides etc then they are safe.
Golfish however suffer with intestinal parasites aswell as external protozoa and flukes,i personally wouldnt feed such fish,certainly not live ones,from frozen perhaps, but thats all.Rays must have a good resistance to many of these parasites judging by how many people feed live goldfish,i just dont think its worth the risk.I can see why people feed these fish to newly imported rays,they will often take them immediately which is often the difference between life and death for many rays that arrive in an emaciated state,if the ray looks to have good body weight and not in a critical condition i would always start them off on the trusty old earthworm if i was going down the live food trail.
As always.......just my opinion.
Sorry for your loss DB.