The !ping plugin does not operate over the chatserver in any way other than being initiated by a command on the chatserver and sending a result to the chatserver.

However, that is not to say that Funcom's firewall won't react. You could end up firewalled from the game/chat server, but that would effectively block all your communication with the servers.

You could be hitting Funcoms flood protection if large amounts of text is being sent in a short period of time. It is not impossible that they have tweaked flood protection with the 1.05 patch.