Bombadil as Aule?

[Lord of Angmar]

The Dark Lord came in right away. The Dark lord was the first in, even.

What else was around when the Valar came in?

"But when the Valar Entered into Eä they were at first astounded and at a loss, for it was as if naught was yet made which they had seen in vision, and all was but on pointto begin and yet unshaped, and it was dark."

Nothing else was around when the Valar came in, save only Eä itself.

How can Tom manage to be around before the Dark Lord when the Dark Lord was the first thing into Eä?

I would say, now, that it is because Tom is Eä, or at least an embodiment thereof.

This quote by burrahobbit on the Derry Dol, Indeed forum backs my original theory, at least in part. I too believe that he is an embodiment, but not exactly of Ea itself but that he is an entity representing the natural world, the kelvar and olvar that abide in Ea.