I'm sorry but this is retarded... If nobody is allowed to use the tank, hydra, rustler or any other special combat vehicle, then it should either simply not be put in the gamemode OR players should not have access to it. If I ever come across such a vehicle that is open to players like that, I'd still rp it, but would involve a "Terrorist" attack on the city or something which is bannable btw, so I dont suggest following my lead...
However, I do suggest to lock these vehicles only to admins or special characters ONLY or just remove them cuz ALOT of these DMers will one day find the location(s) of these vehicles & indeed use them for war, no doubt. But its not right to ban them either... This is not my server though & will have no part in trying to control it either, I'm just simply suggesting ideas here & that's all