I don't know if anyone cares about the original question, but I have heard that local San Francisco shantyman Skip Henderson did the concertina bit for the tavern scene. I've also heard that his song, "Billy Bones" was originally slated to be included in the first Pirates movie (the bonfire on the island scene), but that the powers that be at Disney decided to plug their own music instead.

Can anyone confirm or deny these rumors? Chantyranger?