The answer was a resounding 'no'. There are no such restrictions and if you want to fly a fighter craft and have 2 cargo haulers as your wingmen then good for you. You could even fly a formation of 3 Constellations or, presumably, Corvettes. Due to the way they reference the larger ship piloting, I would hesitate to assume higher.
So, what does this mean? It means that we'll see more flexible game play and some of the discussions mentioned in the Pirate Boxing Theory article could be accomplished without multiboxing at all. Do you know a route that is really safe? Fly a formation of 3 tankers! Have slow reflexes, but still want to do a lot of damage? How about 3 Retaliators! This all rides on the strength of the AI so we'll have to see how they balance this, but the combinations can get really fun.