Forum software is no problem, but live chat scripts are banned. The chat script ban is enforced through a URL filter that blocks the word “chat”.
We don’t ban specific scripts or plugins. MyBB and BuddyPress should all be fine, as long as you’re not using their live chat functionality.
As for why the plugin doesn’t work for you, I can’t say for certain why that happens. It could be a ban on our end but it could also be a problem with the plugin, the installation, or a compatibility issue with our hosting.