I've been waiting for the exact same thing, myself. I was just saying to a friend the other day how nice it would be to be able to style select boxes and file inputs with jQuery UI (and how I wish it had a color picker widget so I wouldn't have to use a separate one, but that's another post entirely).

From what I can gather just by looking at the site, it doesn't look like it supports jQuery UI themes, but the theme CSS for Uniforms looks fairly small and not too terribly involved, so it shouldn't be hard to modify it to match your chosen UI theme.

This is definitely one I'm going to keep my eye on.