Hello PenumbraHulk,
You can feed axolotls mealworms, however you must sever/crush their heads prior to giving them to the axolotl. This is because mealworms, which are the larvae of the darkling beetle, have strong mandibles that are capable of eating through the axolotl's intestinal tract.
Mealworms are not good substitutes for earthworms because they are high in fat and their hard outer shells can result in impaction because the axolotl may have a difficult time digesting them. Thus, mealworms can only be given a treat but never as a staple diet.
Jay.