NeoGAF forum member Sectus supposedly discovered would could be the full roster in the Dead or Alive 5 demo included with Ninja Gaiden III. In the demo, there is alternative costume data that provided strong hints at the roster.
From that data, here's the assembled list:
Kotaku is following up with Tecmo.
Update: A Tecmo Koei spokesperson told Kotaku: "The entire Dead or Alive 5 cast has not been confirmed as of current date, but Tecmo Koei and Team NINJA will have more to reveal in the coming months leading up to its release which is on track for 2012."