1. There are no other available police skins (Tommy and Lance don't work)...
2. Not enough resources to script that, and would take a lot of code. Not needed. You barely lose any significant amounts of health by dropping out of a chopper.
3. Can't apply any other animations than the others built by default.
4. Not needed. There is low interest on ARPD by the community overall so army would have none. Not to say that Army is just an excuse to be a cop. There are no things such as terrorism or wars in Argonath so army is useless.