In moderation, they are fine. Dried mealworms are a concentrated nutritional source - nutrient dense - meaning its easy to throw a diet out of whack with them. Unfortunately, one of the things they are dense in is fat, and excess fat is VERY bad for chickens. Dried mealworms are often identified as being 25-30% fat. A chicken's diet should be about 3.5% fat +/- daily. Functionally, that means that 0.4 ounces (about 11.5g) of dried mealworms represents a chickens entire recommended fat intake for the day. No, your chickens won't die if you accidentally feed them 4% fat for a day - in fact, fat recommends for waterfowl like ducks are around 4.5%, and Cx (Cornish X, raised for quick table, not longevity) are often fed 6 or 7% fat levels) - but fat can build with time, and its far moredetrimental than a slight increase in protein is beneficial.
So use it only as a treat. Similar to a vitamin at home - one a day , not a plate full. (its actually a couple of dried mealworms a day, but you get the idea)