Any way to make dijit.Editor form elements "required" ? Have it trigger an invalidMessage call if nothing is entered ?
i.e. like validationTextBox ?
required="true"
invalidMessage="Please enter a value."
I can write my own form validation script for just this one field, but since I am already using validationTextBox it would be nice to have all the validation messages on the form look the same.

dijit.Editor isn't a form element...
at least it isn't yet, though there have been many requests for this, and the functionality you describe is only baked into widgets derived from ValidationTextBox.