creole is a wanna to be standard markup for all wikis.
It's an agreement archived by many wiki engine developers.
Currently MoinMoin and Oddmuse supports it. And a lot of wikis (dokuwiki, tiddlywiki, pmwiki. podwiki, etc) have partial support. More info on support: http://www.wikicreole.org/wiki/Engines
Some useful infomation:
And there is a perl module: Text::WikiCreole
Syntax file for vim: http://www.peter-hoffmann.com/code/vim/ (Since a typical ikiwiki user usually use external editors. 
Should be pretty easy to add a plugin to do it using > Text::WikiCreole. --Joey