I would think the call to the supervisor would be initiated if there was just a minor but too-serious-to-ignore violation. But if an officer were driving in a way to place others on the road at risk, another officer would be fully justified in pulling him over to minimize that risk. There was some media coverage over something like this back before the first of the year, I don't recall the jurisdiction, but several officers were traveling to a training seminar of some kind, and several civilians video'd them really flying low, 100+ MPH, w/o emergency lights or sirens. Somebody called the appropriate authorities, and a few of them did indeed get pulled over. No idea if they were cited or just given a word to the wise. I wish I could recall more details, caught part of the story on GMA, didn't have time to look into it.
Just my $0.02, I'll crawl back into my mudhole now...