A federal law that doesn't allow commercial driver to carry is a myth. I researched this quite extensively when I was driving OTR. The only law that applies to guns in commercial vehicles only applies to passengers.
(e) It shall be unlawful for any person knowingly to deliver
or cause to be delivered to any common or contract carrier for transportation or shipment in interstate or foreign commerce, to persons other than licensed importers, licensed manufacturers, licensed dealers, or licensed collectors
, any package or other container in which there is any firearm or ammunition without written notice to the carrier that such firearm or ammunition is being transported or shipped; except that any passenger who owns or legally possesses a firearm or ammunition being transported aboard any common or contract carrier for movement with the passenger in interstate or foreign commerce may deliver said firearm or ammunition into the custody of the pilot, captain, conductor or operator of such common or contract carrier for the duration of the trip without violating any of the provisions of this chapter. No common or contract carrier shall require or cause any label, tag, or other written notice to be placed on the outside of any package, luggage, or other container that such package, luggage, or other container contains a firearm.
So if I was a driver of a commercial vehicle any passenger I took on would be required to hand over his firearm to me. It does not restrict the driver.