Thanks for the feedback, everyone.
As for the Big Red Worms at Walmart. They are red wigglers. They are safe to feed and my some of my frogs with eat them (they piggies will eat anything). Yes they are a more manageable size for ACF, but they produce an irritating mucous when disturbed. A lot of frogs will be put off by this. My African Bullfrog really hates it, so much that he refused all worms for a while. I finally got him back on nightcrawlers and will never buy the wigglers again.
So, yeah they are safe to feed, but you run the risk of deterring your frog from eating all worms if he doesn't like the irritant from the wigglers. You would be better off looking for smaller nightcrawlers or cutting them (it's gross but it works).