Aren't xbla ports mostly PC ports? So that would suggest VF2PC version as base.
So the SEGA Xbox Live Arcade ports have been from a lot of different sources over the years. For the most recent titles:
- Sonic Adventure -- Port of the PC version of the game, with the DX additions made into DLC. Kept to 4:3, very little done.
- Crazy Taxi -- Port of the PC version of the game, with the soundtrack changed from the original and brand name places removed. Little done to it at all.
- Space Channel 5 -- I'm going to say it's a port of the PS2 version of the game, as there was no Dreamcast English release.
- SEGA Bass Fishing -- I'm going to say it was the PC version? Not sure.
- Sega Rally Online Arcade -- Port of the Arcade version of the (originally) retail title.
- Virtua Fighter 5: FS -- Port of the last Arcade version of the game, modified to split costumes etc into DLC.
- Daytona USA -- Port of the Arcade version of SEGA Racing Classic, a port of the original Daytona 1 Arcade to HD monitors, but switched back to its original name.
- After Burner Climax -- Port of the Arcade version.
- House of the Dead 4 (PSN) -- Port of the Arcade version with PSMove additions.
- Sonic Adventure 2 - Port of the Gamecube version of the game with the "Battle" additions used for DLC. Made to fit widescreen and be actually HD.
- NiGHTS - Port of the Japan Only PS2 version of the game which had upgraded visuals.
- Jet Set Radio -- Ported from the Dreamcast version, given a rather significant upgrade to suit HD resolutions. These games aren't emulated either, they found the code (or most of it) for this stuff.
Sonic CD -- A complete rebuild of the original Sonic CD Mega CD version, vastly improving a lot of emelents including making it actually widescreen and playable Tails.
If they've been able to port over NiGHTS from the SEGA AGES collection, it would make sense that Virtua Fighter II and Fighting Vipers are the same deal. They're upgraded slightly and they'd probably have the source for that stuff around.