Are you guys talking about that commercial dreamcast-based playstation emulator called Bleemcast? That's the only boot-disc thing I can think of that was an official release.
Sega didn't care about it, but Sony sure did, sued the company a couple of times. Sony lost those lawsuits, but the court costs effectively put the company that made Bleemcast out of business.
It only ever ran a handful of games, but according to the courts it was 100 percent legal.