Wikis that support RSS and wish to make that fact visible can create a wikipage, preferably WikiRss, that is linked from somewhere in the wiki.
To enabling searching, that page should include the following URIs:
If you have control over the RSS, using 1.0 will indicate the channel topic (some category) or individual entries are about some category.
A few text keywords you want the search to pick up on for your wiki overall. If your wiki is about snails, include the word "snail" somewhere on the WikiRss page.
You can register with various RSS search engines or listing services (i.e. syndic8.com) so people can find them easier.
A cool idea would be to have every wiki word referenced in a wiki pages, or maybe just those that start with category, as metadata for an item entry.
The channel might have the dmoz category for the wiki overall.
"The RSS 1.0 Wiki Module is an extension module for RSS to describe metadata particular to wiki applications. As such it's an XML application conforming to the W3C's RDF Specification and the RSS specification of the RSS-DEV Working Group."
See ModWiki.