Just a wild take: the man is Willy Garon.
Willy Garon was a scientist (more specifically, a physicist) who was quoted by the narrator in chapter 218 by this words: "Anything man can imagine is a possibility in reality". It's very weird that Oda felt like doing something as unusual as having the narrator quoting a character we haven't known more about since then, specially considering this Willy Garon guy pretty much explained what was recently brought up again by Vegapunk and imagining devil fruits into existence.
What if the scientist Oda said would explain everything about devil fruits wasn't really Vegapunk but Willy Garon since day one? Chapter 218 is quite important because it establishes Robin joining the crew, tells about the Poneglyph and hints at Skypiea (an island with obvious importance regarding the bigger picture).
Now, about why I think the man could be Willy Garon: "black ships" is how Japanese people named the Western ships that reached the country for trading back in the XVI century*, but also the popular name given to the ships of the Perry Expedition (which intended to open Japan's borders); these ships were called "black ships" (kurofune) because they used coal-based steam engines. This industrialization of the black ships is what leads me to believe the man's black ship may be scientifically enhanced and the man himself a scientist using technology to create the whirlpools.
If nothing of what I just theorized is true, then I'll also add that Willy Garon isn't the man with the scar but the scientist who either created or researched devil fruits during the void century.
* More interesting information on this, take it as you wish: Goa was the name of the headquarters of these Western traders (Goa is where Dragon was born, since he has been proposed as a candidate too)