According to detective Ausir ButtFace Mcgee;

According to an anonymous, but fairly reliable source of mine, developers at Obsidian are not the only people who worked on the original Fallout games and are coming back for Fallout: New Vegas. Mark Morgan, who composed the Fallout soundtrack and Fallout 2 soundtrack (as well as the music for Planescape: Torment) is reportedly working on a project for Obsidian - and I highly doubt it's Alpha Protocol.

I, for one, hope that the rumor is true. Stay tuned for first official New Vegas information in 3 weeks from now.

You can see the Ausir entry here.

DAC contacted Mr. Morgan to see if the rumors were true. He debunked them, however.