If you knowingly tinker with a system you're not supposed to have access to --- that is, you either VNC into a system that isn't yours and see things that a reasonable person would react to as an indication that they weren't welcome, or that a prosecutor can claim a reasonable person would react that way to --- you're violating the CFAA.
All current indications are that scanning the whole Internet for open VNC systems is, if not lawful, then at least so close to the line that nobody's going to make an issue of it.
But logging into a VNC server and poking around crosses a bright line. Arguments about the implied welcome given by lack of a login screen will probably not persuade a jury, let alone a prosecutor.
The idea of hooking open VNC servers up to a "roulette" game seems beyond stupid. Maybe someone's thought about this more carefully than I have and can explain why I'm wrong?