I was wondering, is it bad to rev the engine on a hybrid car?
Also what would happen if I did rev the engine. Would the battery be used or would the gasoline engine start.
The short answer is no. Revving the engine in neutral (if the car will allow you to do so) will cause no damage.
Most Hybrids I have driven will only start the engine if you fully depress the accelerator in neutral. Even when you do this, the engine is only ticking over and wont rev higher unless it is under load.