It's recently been confirmed that Alan Scott / Green Lantern will be appearing in the Legends of Tomorrow season finale. It's also been revealed we won't know Iron Mask's identity until the Flash season finale. I've come to suspect that Iron Mask is a younger version of Alan Scott and the Legends of Tomorrow finale will feature an older one. Also the place Zoom has Iron Mask captive looks like it was an abandoned railroad of some sorts and Alan Scott was a railroad engineer. This would make sense if they introduce him in Legends and the following week introduces him as the Iron Mask, so he gets to meet Team Flash and we already know a bit about him. What Zoom said about him to Barry "you wouldn't believe me if I told you" may be because they wouldn't believe what he is if he tried to describe Green Lantern's powers. I don't know why Zoom has him in an iron mask captive but I'm assuming he wants his lantern ring, or maybe he knows something about the real Jay Garrick. I don't doubt we'll see the real Jay Garrick at some point and I hope it's Teddy Sears playing him too, but I don't think he's the Iron Mask.