Yes and no.  Many people use mealworms as feeders with no ill effects at all,
especially with lizards.  However, mealworms have hard chitinous shells and
may cause digestive problems in large quantities.  Moreover, mealworms have
mandibles; at least one poster reports having seen mealworms literally eat
their way out of a garter snake (yuck), and this author has lost leopard
frogs to internal injuries caused by "king" mealworms.

The chitin problem can be almost entirely ameliorated by feeding mealworms
that have just shed their exoskeleta.  Since they shed their mandibles as
well, this procedure should also help with the problem of internal injuries;
however, if you're feeding mealworms to an animal that can reasonably be
expected to swallow them whole, it is prudent to cut the worms' mouthparts
off first, or to crush their heads and mandibles with a pair of forceps.
It's not pleasant, but it beats risking your herp's health.