Incorrect. In order to drive ANY Federal, or Postal vehicle, the driver is REQUIRED to have in his/her possession a valid Standard Form 46, which is the driver's license.
How do I know this to be a fact? Simple. During the course of my military service, one of the duties I was responsible for was the issuance of those same Standard Form 46's.
the infowarrior
U.S. Supreme Court Says No License Necessary To Drive Automobile On Public Roads
Numerous Cases