Yes your RV Air Conditioner can be used to cool off the RV while driving down the road.
You'll just need to start your on board RV air conditioner and supply the electric to the RV air conditioner.
Just keep in mind though that when you run the RV generator to run the RV air conditioner that you will use more fuel so you'll need to refuel the RV fuel tanks more often than you would when just using the fuel to fuel the RV engine.
So your MPG will drop because the on board Generator will be using some of the fuel to run the generator.
But other than that there's nothing wrong with running your RV generator when going down the road as many people do run their RV Generators and RV air conditioners when traveling down the road and it never has been a problem.