Hi Charles,

The standard built-in date type has the format of YYYYMMDD and can be overridden only by using external grammars.
 
I dont remember the exact path or the file but you might find the built-in date grammar for Nuance somewhere in the subfolders of the Recongnizer, you can give a try to improvise on the available grammar file that takes in YYYYMMDD and modify it to consider MMDDYYYY and then as you suggested you can use a form element with this external grammar to capture the date input.
 
Hope this helps,
Ranjana.