Considering the Black Major is carrying that the Club called "the sign of leadership in the Red Shadows" (ie that whip), I'm guessing he's not Ironblood since he's not carrying said sign of leadership.
Also, having Interrogator just be Ironblood in disguise would be dull.
But then again, I'm not a fan of Interrogator having a removable helmet, because it removes all the mystique around the character.