I'd have to give Frank more than just mere agreement. Singing is a language & slaves used it to the max. In the song Ol Riley, I asked the Georgia Sea Island singers who was Riley thinking it may be a possible connection to "Riley" of found in sea shanties. I was told that Riley was a slave driver, kinder than most others & that's why they would rather leave with Riley rather than face a new slave driver that they didn't know & would alomst assuredly be much harded on them. Riley was his nickname & so his real name couldn't be used but everyone knew he was going & who he was. Go to the prison work songs the language was used there to & againg their white oppressors didn't care to listen to the songs never mind the content as long as the work got done & they (the oppressors) knew the work would not get done as well or as effeciently without the singing. Like shanties you could sing whatever the hell you wanted without fear or reprisal.
The slave communication network was quite vast but simple. Their communities knew more of the world boarding the Alantic Rim than probably most of their white "betters". They were constantly being shipped or worked in ports where they had all the lastest news, this was their mail route & their telephone line, they would know who made it safely to the north, they not only worked the waterfront & ships they worked their own form of infomation pipeline too & they worked it very well.
For more on this see "Black Hands, White Sails" by P & F McKissack pub. by Scholastic Press 1999 & "Black Jacks-African American Seamen in the Age of Sail" b W Jeffrey Bolster pub. by Harvard University Press 1997

As Frank mentions there are plenty of examples where slave songs sing of how to carry oneself, how to behave, how to survive, how to cook, how to hunt & how to find one's way to freedom & how to dance.
Another good resource, although from a slighted view is "Slave Songs of the Georgia Sea Islands" by Lydia Parrish, pub. by the University of Georgia Press 1942

Barry