From personal experience when on duty I have found that two things are true, number one if I am in a dangerous situation anyone who comes up to help would always be appreciated. The second thing would be a collary to that, being if a person comes to help and acts like a cowboy all he does is put us both in more danger. In my second job (which is security) I have numerous times come across a cop in a bad situation and had no hesiation with stopping and helping him or her out, main thing in that situation is not overstepping my bounds.