This isn't quite true. I've hacked pretty hardcore on a single PB-Disabled Ranked server and I wasn't banned.
However, if you are playing on them, it will likely arouse some suspicion. The suspicion may lead to an investigation which would show that you are hacking.
Also, since it is ranked, you'll find that your insane stats are put onto your account information for all to see.
If you obtain a 200:1 KD/r on a ranked no-PB server, you're still likely to get banned for that alone.
Playing on the server won't lead to a ban, but hacking anywhere is always a risk.
The fact of the matter is: You're less likely to get PB auto-banned on disabled servers (100%) but you're more likely to be manually banned.
Hack safe, guys.