We checked with Namco on the matter, and can now happily confirm that it is the former case.
"The game is based on the Dreamcast version with no major additions or subtractions," said a Namco Bandai representative to Shacknews.
Look for the 'Cast-derived, high-def Soul Calibur to hit Xbox Live sometime this summer.
This was my favorite SC of them all. This should be pretty sweet!