This guy is out off the south coast of Azshara near Durotar. He's in a sunken ship so close to The Great Sea that your fatigue bar will pop up if you're out parallel to the ship but not on it.

I have no idea what he's there for.

Captain Vanessa Beltis of the Horizon Scout will tell you that her ship was attacked by naga and sank. She is located on shore, and gives a quest to defend her from a naga attack. She mentions that other crew members may have tasks for her to do, but none of them give any quests.

Roland and several other unnamed members of the crew remain on the sunken ship (with use of an underwater breathing spell), but do not give quests or otherwise interact with the player. The ship itself is off the map; follow the floating wreckage directly south of this point.