Yes it is. Any attack on the enemy is allowed if that attack is done from a hog that is properly racing. The rules come into question when either the attack is not from a hog (the player is on foot) or if the hog they are in is not racing properly (camping or chasing kills). As long as everyone is racing properly then it is "game on", take the enemy out!!! I will say this though. Nading from a side seat, especially long shots or blind throws, rarely hit their target and can in fact disrupt team mates. For this reason we ask that you not "spam" nades from a passenger seat. If you have a legitimate target and a reasonable chance of hitting it then go for it but don't go nade chunkin just because you can.
