Just like the Pighead from the previous game, Pighead II's real identity is never revealed, or why he is working for Jigsaw. However, Sarah Blalok, who was a neighbor of David Tapp, told Tapp's son Michael that he knew the man behind the mask and that he was a friend of his father. But before she can reveal his identity, she was killed by Joseph Poltzer.
It is possible the person is Mark Hoffman. In case files in the game, Tapp reveals that Mark Hoffman was one of the few cops he had actually trusted (ironic considering he is working for Jigsaw). It should be noted that Pighead stabs and kills Henry Jacobs (a corrupt chief of police) in a similar manner to how he disposed of officers in Saw 3D.
Unlike the first Pighead, this one isn't hostile to the player (most likely down to his apparent friendship with the character's father).