Can I have a single non-viewable field in a form?

If you create a form with a single non-viewable form field, the form will still be displayed to the member, but with no information in it. So, if you really want to have a non-viewable form field (e.g for storing internal information about the member), then you will need to come up with a form field that will be viewable, so that the member is not confused by a blank form.