A Unity Form can be submitted when a required field is empty
"When a keyword is set within the Unity Form designer as both 'Read Only' and 'Required', the form it is on is able to be saved within the Unity Client with no value in the field", was created to address this issue, but it was determined this is functioning as expected.
Per the "Properties" section of the Unity Form MRG:
"If a field is configured to be both read-only and required, the required setting is ignored. In the event the field is not populated automatically, the form would not be able to be submitted if the required option was respected because the field could not be edited so that it contained data."