I have cops back on the beat, they will assist you if shots are fired, they dont technically know your a cop, or that your even part of the situation, but they just target the guy your shooting at because he has a gun, it goes off native combat behaviour, its just a coincidence that your "helping" I hope you understand what Im saying aha :) They wont help you in a persuit, unless shots are fired either, but thats why you have LSPDFR backup options :-p