Backgrounds were extremely diverse, from Ivy-league graduate math majors to a former horse trainer. The graduation rate was around 85%, and among the graduates, the 'true' job placement rate was probably around 90%. I was able to hit the ground running in my first software engineering job at a well funded startup, and was on par with other fresh cs degree graduates. Over the next few years I was the first among that class to be given a team leadership role.
Looking at LinkedIn, the other graduates from my bootcamp seem to be having their own successes at FAANG jobs and other strong positions. While I believe my experience was somewhat typical for my bootcamp cohort, (like college) I think quality can vary greatly based on the bootcamp, and I am sure some are bad deals in the ways Zed has outlined.
edit: For those who are wondering if the successful bootcamp grads would have been successful anyways without the bootcamp - 100% no way for me. I had already been self-studying programming before the bootcamp and it was a night and day difference. It would have taken years of self study to learn what I did, and with a good chance that life would have derailed me along the way.