Vic wasn't technically bullet proof at all, he was just damn real unkillable. The bullets tore through him and even as the pain flared then faded withing the blink of an eye, his body still reacted instinctively.
That the other was smart enough to take advantage of his tiniest weakness cast him in a light that Vic appreciated. He wasn't a slacker by any means and Vic felt that the other was the kind of guy he'd call a friendly companion if the circumstances were different.
He wasn't sure if he'd lose interest or tire first, but so long as his prey had ammo he wasn't going to land a decent hit.