The new Eureka release for ServiceNow supports persistent search for non Active Directory servers. Woo!
However, you enable the listener and you get the error: "[LDAP: error code 12 - Unavailable Critical Extension]" Boo!
Turns out that when you configured your LDAP server ages ago, you may have set the 'Vendor' field to be 'Active Directory' because, hey, that was the default or you wanted to see if changing the vendor field did anything. Since it didn't, you may have forgotten to change it back. It doesn't help that the server configuration page doesn't show this field (so you probably want to add it back to the page).
After changing the vendor to 'Other' (the only other choice), the error doesn't seem to be occurring now. Now, the fun part to see how persistent search interacts on imports.