Yes all the Pirates can communicate, most games they can. But if you can take out the power roles it diminishes their strength. Actually we get the Captain and its game over.
The Gov and Mag can communicate, if the Thief finds the Mag they can communicate. The Mag can also communicate with the Watchman but the watchman can't communicate with the Gov.
Its all actually a bit confusing but I'd assume the Mag would tell the Gov who the Watchman is even if they can't talk also any thief that might find the Mag.Uhm...I read that the Mag wasn't allowed to reveal who the Watchman or the Thief are to anyone...and it would behove him not to reveal who the Gov is.
This is also why 1st night votes help out with other days as it helps show links between players.
My comments above.