Mat is a Hero reborn. He is ta'veren. It's my belief that all ta'veren are bound to the wheel, for the Pattern to spin out where needed. He didn't meet a previous life when he blew the Horn, though. All the Heroes who responded were the ones not currently incarnate. Since Hawkwing and Gaidal Cain were there, I think we can rule them out as being Mat's past selves. Another thought is that no, Mat is not a Hero of the Horn. It could be that he, Rand, and Perrin are three ta'veren the Wheel keeps for the express purpose of fighting the DO. This leads into my Forsaken theory. My thoughts are that all the Forsaken and Rand are in a group of souls that are used over and over again in the battle against the DO. But, what changes each age is which one of them gets to be the Dragon. Ishy once told LTT that they had fought alongside each other for the Shadow. But, Mat and Perrin are always there to help the Dragon in the fight.