I love a thread that wanders around all over the place, and gets back on the original subject.And keeps on keeping on.

Even if whatever whoever came up with the line originally might have had in mind, in practice it'd be pretty inevitable that the sailors doing the heaving and the hauling would have taken it as referring to them, and the shantyman would have meant it that way.

Calling sailors Kings of the rolling sea had the same kind of logic as calling a tramp a "King of the Road" - and as with could be taken or intended either way, directly or ironically.