Have you tried it? If you have Vista-ready drivers from M-Audio, I believe the integration with MC's ASIO implementation should work.
However, the Vista32 drivers are beta (Version: 5.10.00.5065), and there's a note on their website that "DTS pass through does not work at the present time with Vista 32, AC-3 does work. The problem is restricted to Windows Vista 32. DTS works fine with Windows XP. Does not apply to the Delta 44."
So, things are clearly in a bit of flux with M-Audio. I've had a DiO 24/96 card for years that I love, but went with my integrated SPDIF output when I moved to Vista.
I say give a whirl and let us know what happens!
(Make sure you have the correct channel offset, though, or there will be no sound....)
brad