Yeah, IANAL, but this isn't a court. Things don't need to be admissible to be used by private citizens. It doesn't matter how you got the information, it's only libel if it's false and you had no reason to believe it was true when you said it (basically, if you just said it for the lulz). Also, its only defamatory if the primary purpose of the statement was to publicly attack someone. If the primary purpose (as here) was to expose a business practice, and your reputation just happens to get slaughtered in the process, then maybe you shouldn't have been working for a shitty company.