No, it's not true. They are not the absolute worst feeder and can be part of a varied diet. They are a better option than mealworms! Just don't use them exclusively.
I don't know about that, superworms are usually okay. My reptile store told me they are not awesome, but they work when you are trying to add variety to the diet. He gave me dubia roaches instead. Honestly, I never heard anything like that and I am constantly seeing posts about veiled chameleons and superworms in their diet. Just not as a primary food source. Maybe more people can give better answers than me. Oh it looks like @Decadancin already handled it