I was taught to give a short verbal warning (stop, don't move, drop it...two words or less). I was also taught that a CCW holder is responsible for every round that they fire, once a bullet is fired nothing can be done to bring it back.
If the definition of warning shot is to intentionally miss the target then I have to say it's a bad idea for a lot of reasons, namely because you cannot control where that stray round goes. Also from my experience if your first shot is bad following it up with a good shot is more difficult and takes more time to adjust your aim.
BUT in all fairness if it reads "unless hostilities are already in progress" I wouldn't worry about it too terribly much, most states do not allow you to draw your weapon and fire unless something bad is already happening or imminent. Just my opinions, I'd look more into the already in progress clause and clarify it's definition and intent with a CCW trainer or the local authorities.