Hey Pete and Rich,
I found an interesting tid-bit in the MLBUM, Section IV - Conduct and Responsibilities of Umpires:
IV Standards for Removal from the Game.... one of the points reads:
During an argument if a manager, coach, or player makes reference to having observed a video replay that purportedly contradicts the call under dispute, such person is subject to immediate ejection from the game.
So if the manager wants to appeal and admits to hearing the PA Announcer, he too gets ejected too under OBR!
Also for the PA Announcer, the MLBUM says:
2.24 PUBLIC ADDRESS ANNOUNCER
The public address announcer shall make all announcements that are directed by the umpire regarding lineups, Official Baseball Rules, and other pertinent information. The public address announcer shall make such announcements immediately as directed by the umpire. The public and the media should be informed if there is an unusual or technical play or incident during the playing of a game.
In order to avoid confusion, public address announcers are not to announce lineup or substitution changes until the plate umpire signals such to the announcer. Violations of this policy are to be reported to the Office of the Commissioner.
I could find nothing else.