Actually, MisterBetta, while I understand how you feel perfectly(I can't even go fishing if I have to use live-bait, lol), bettas really shouldn't be on a completely plant-based diet I wouldn't think. They are carnivorous/omnivorous and need meat of types to survive in most cases. Live food isn't the only option if you have bettas - betta pellets work fine, as do freeze-dried food. I feed these to my bettas and they're all just fine. On the other hand, though, they will in fact eat some plant matter, too - I keep some corydoras catfish(cory cats) in with a sorority of bettas and one male, and occationally drop in an algea pellet... and I just can't seem to get them to leave the things alone! Alongside that, I also have a very large amount of trouble growing water lettuce, and I think the bettas are partially to blame. I know at least one of my males eats/nips off the roots of the plant.
So while I understand that you don't like killing things, as I'm in the same boat, I feel it's important you find some food product to feed them so they get those nutrients. ;) I'm sure your bettas are healthy, but I bet they'd like having some suppliments.
But on the actual topic, I'm not sure as I've never heard of superworms, but I'd still be careful because yes, live food can cause parasites... I'm not sure about these but I do believe it's the blood worms that can cause dropsy. So that's something you'd wanna be really careful for(A dropsy-sick fish is a dead fish).