I've always used oatmeal and never had any problems whatsoever. The biggest disaster I've ever had was taking the advice of another dealer I met online back during the Superworm shortage who told me to use spagnum moss. I bought high-quality orchid spagnum moss and spent the next month looking for Superworms like proverbial needles in a haystack.
You've got me curious about the cornmeal.
Ann