No, it's not true.
Frozen BW typically consist of 80-90% water, so not only are you mostly paying for water, when your fish consume them they are mostly consuming water. IMO if you want to feed worms to your fish you're better off growing your own red worms.
Here's a typical analysis of frozen BW.
Guaranteed Analysis:
Crude Protein (min) 3.5%,
Crude Fat (min) 0.3%,
Crude Fiber (max) 0.7%,
Moisture (max) 93.5%
Fish love them & readily eat them because they taste good, but nutrient wise they don't offer a whole lot.