I don't think there's a blacklist system in all official chats.
However, I completely understand the reason why someone can be "blacklisted" even if they said something offensive in other chat or if they've had unprofessional or embarrassing behaviours in other chats and not necessarily in the chat where they want to get a rank. I run an official chat, and I would never give a rank to people with such behaviour. Having people with such behaviour as staff members can easily create an unnecesary negative perception of the chat. That's the reason why some people can be blacklisted even if they didn't do anything wrong in the chat where they're trying to get a rank, and I'm sure most chat managers would agree with what I'm saying.
Furthermore, that's not the only reason why someone can be blacklisted, toxic people are usually blacklisted too, or at least that's a reason for me to blacklist people, even if they were staff members in the past.
Anyway, there will always be abusive chat managers that won't act fairly, and that's a fact. If you feel that a chat manager acts unfairly, you can always report them.