I got word back from Akismet that using it on UCalgaryBlogs.ca to protect all of the blogs hosted there falls under the free license, despite the wording on their website that suggests it's an enterprise use. This means I'm now able to protect all blogs on the service with Akismet, without requiring a Captcha challenge.
The current version of the Akismet plugin for WordPress installs just fine in the mu-plugins directory, meaning each blog automatically gets protected, without any configuration or setup. The Akismet key can be hardcoded into the plugin file, and when that is done, all configuration interface magically disappears from the wp-admin interface. Easy peasy.
All that was required by Akismet was that I provide a link from each blog to Akismet.com to give credit for the spam protection. I wrote up a VERY simple mu-plugin to automatically insert the text and link in the footer of each blog on UCalgaryBlogs.ca.
I'm curious to see how well Akismet functions on some of the topics of conversation - some post colonial courses commonly use language that trips up word filters pretty readily...