There is a real need for it. Players could play between one another and enjoy themselves. The purpose of a paintball in real-life isn't for LEO training, but rather type of entertainment.
Having this arena is not going to be "a paintball server", but rather give something outside of the normal role-play or just driving around. Yes, this could escalate into server-wide events and become server tournaments and whatnot, but it is very ignorant of just saying "no other real need for it, but PD and SD". You make this look now like PD/SD server, and everything should be for them only, otherwise there is no need for it. You can make that people need to pay for it and so on, just like you can go in real-life and shoot some paintballs at your friends, or take it competitively.