I fed them to my newts for a while, and they digested fine, but I was always careful to give newly-moulted larvae. If you have enough mealworms and you dig around in the substrate for a while, you can probably guarantee coming up with a few that have less chitin.

But again, that's newts. I fed some really small mealworms to one of my tree frogs for a while, without problems, but that was just a stopgap while waiting for crickets. No issues though.