The plugin supports taxonomy terms from the category only. To enable this feature goto the options page and enable “Category Facet as Taxonomy”. Save changes and reindex your documents.
The current version of the plugin has not been tested with WPMU, however, the new version which will be released shortly has WPMU support. While adding this support, I ran into this same error. Turns out is was a problem in WPMU itself and has since been fixed in recent version. Update your WPMU version and you won’t have this problem anymore.
The plugin is not dead and a completely new version is about to be released. There is a few things I have yet to complete, however, it should not be to much longer. To answer you original question, yes the plugin supports this type of faceting. Goto settings and enable “Category Facet as Taxonomy”. Save the changes and reindex your documents.
