Well theoretically he could be a Vala then, but he doesn't really have the characteristics that all the other Valar have in common. And also in the Council of Elrond it is said that Tom Bombadil alone would not have the power to defeat Sauron and that he would fall as the last person in Middle-Earth if the council gave the ring to him. So I don't think that he is a Vala, because Sauron is a Maia and it is said that the Valar are more powerful than the Maiar so if Tom was a Vala he should be powerful enough to defeat Sauron in my opinion.