Hi,
One of the devs for 'GeSHi - Generic Syntax Highlighter' replied back and offered to include the nginx language file in the official distribution if someone is willing to cleanup some of the issues preventing the file from passing the language tests:
http://sourceforge.net/tracker/?func=detail&atid=670234&aid=3554024&group_id=114997
I don't feel I have the necessary skills to do so, but I plan on giving it a shot when I get a chance.