I don't know a whole lot about wikis, as I've not really ever had to use one, but looks like your main problem is going to be finding one that supports Oracle.
It might be overkill to use a CMS, but have you considered using Drupal with the wiki module? I started using Drupal for a similar purpose a while back, but gave up on it. Now I've been using Drupal quite a bit for recent projects, I've considered trying it out again. It's got a steep learning curve, but it's quite flexible.
Your problem with Drupal would come with implementing it with Oracle and integrating it with your existing extranet signon.
One I've come across that's not in your list:
wikkawiki. It's lightweight and may suit?