They most likely did in the past, but modern labor laws and HR practices would make that very risking for any participants.

But there are still a few CP bro networks out there, and any wholly-owned regional will obviously share personnel info with mainline.

If you get on somebody's blacklist, there's no way off. There's also no way to find out that you're on one since they would be "unofficial". Somehow you would have to get enough info to justify a lawsuit and subpoena. "They won't hire me" is probably insufficient cause.

There are probably official "do not hire lists" of people who have applied and/or interviewed but been deemed unsuitable and not eligible to re-interview, probably due to suspected ethical or perhaps personality issues. In most cases an unsuccessful applicant can try again after some period of time.