I'm not sure you can count it as an actual ability because there was never an explanation for it, but yes, he's ridiculously lucky (Other than the whole forceful conscription into the Spartan program thing) and it's something that's been consistent and noticeable since he was a kid, including for coin tosses. It's why Cortana chose him over the other Spartans.
It's basically their justification for stuff like him never being on the ship instantly vaporized by the giant laser beam or in the facility hit by a nuke.
That's not why he knew the result of coin tosses. His vision was so good that he effectively can watch the coin flipping and know how it landed.