You can shoot out of an offroad if roleplay HAS been initiated before the chase happens.
For example if the police sound their sirens and you attempt to shoot them with NO roleplay/ shouting out of the car then it would be considered RDM/ low or poor quality roleplay. However you can shoot out of the offroad if beforehand there is an ongoing firefight/ they issue compliance and decide to chase you whilst shooting then you CAN shoot out of an offroad.
May I add, if you hit someone that isn't in a vehicle, they will only be knocked down and the anti VDM script will kick in. But if they're also in a vehicle, you can do damage to them.