Tyne has updated his Quake mod that works on Xbox and Dreamcast.

Grab it here:
High-end Darkplaces version:
http://renegadec.digitalfunk.org/Quake%20Mods/StealthDP.rar
Text:
http://renegadec.digitalfunk.org/Quake%20Mods/StealthDP.txt

Low-end Winquake version:
http://renegadec.digitalfunk.org/Quake%20Mods/StealthWQ.rar
Text:
http://renegadec.digitalfunk.org/Quake%20Mods/StealthWQ.txt

I've tested the Winquake version on Xbox which uses nearly the same engine as 
nxQuake, so it should work on Dreamcast; it'd be nice if someone can test it 
for me to be sure though.

Source: DCEmulation forums