Digital Nightfall on 28/2/2011 at 15:52
Many of the games Warren was producer on have similar references to him. It's possible that the maker of this game was a fan. It's just as likely to be a reference to Martian Dreams or Serpent's Isle as underworld. Still a pretty cool find, though.
I believe Warren is also featured in a deck of "geek icon" playing cards as well. Not sure what card he is, though. I saw it last week but forgot to save the link.