Charlotte, NC used to have a Midnight Moonlight ride. After the pro series of criteriums downtown, hundreds, maybe thousands of people would mount bikes and ride an 18 mile loop through the city at midnight. Great fun! Lights were encouraged, but the vast majority of the riders just had rear blinkies. It is no longer an event, my guess is the insurance risks, and large crowds scared off the organizers.

A few points of safety. You will have a hard time seeing cracks and potholes in the road. You will also have a hard time distinguishing crackheads and potheads in the crowd. There will be a percentage of riders that will spend the hour or so before the ride trying to drink all the beer they can find. They may present a danger as you ride the course. There will also be many young children and people that are unfamiliar with bike handling skills and maintanence requirements, beware!
If you take the ride at face value, a nice slow easy pedal through the city, you will enjoy it. If you decide to approach it from a racing standpoint, starting last and seeing how many people you can pass, you may encounter problems along the way.
I have done the Charlotte ride from both standpoints. A good friend ended up spending the morning hours in the hospital getting a broken collarbone treated the year we decided to start last and finish first.