From a very lay perspective. OSHA is more about like, pathogens and shit (health concerns, basically, lots to do with regulating chemicals/solutions and exposure) but could potentially also address things like sleep/time allowed to work nonstop (like truck drivers). CDL license is definitely gonna be a Department of Motor Vehicles/cop thing - if the driver of a truck were pulled over and didn't have a license I assume both he and his employer would be in deep shit for essentially driving w/o license, etc. As for the safety of the truck or how the truck is being used (safe vs. unsafe conditions), not sure about that. Could maybe be OSHA, but feel like there should be some other set of regulations that covers it. Course, out in the middle of bumblefuck with no cops around to catch road safety violations, probably pretty easy to violate without consequences.