How does their business model work with subpoenas? If the police don't pay to use them, but the camera witnesses a crime, can't they get a judge to order the video because it's evidence in a criminal investigation and/or trial?

What about a civil case? Can an individual get a court order for flock to release evidence that it may have (or definitely has) relevant to a divorce case or other lawsuit?

They evade accusations of constitutional violation because they're a private company. But other private companies have to turn over records all the time (credit card purchases for example).