No, Tom's origins are never really revealed, but he's not of the orders of the Valar or Maiar; he is, if anything, similar to the Genius Loci of earlier metaphysics. He has no allegiances, and is wayward and unpredictable, impish (though not necessarily mischievous, and certainly not evil), like some of the smaller nature deities.
The symbolism of Tom is quite complex, I think, though it takes a careful reading of the text to get that, as it seems at first glance simply an odd digression; but he symbolizes many aspects of Tolkien's views of "unfallen" nature, I'd say, as well as his roles given above. I've come to find him more and more of a fascinating character, yet he still remains rather enigmatic....
