Neither the standard nor the advanced search forms in the admin interface offer an option to search for hidden objects.

Unluckily the code in policyLimitationFilterQuery, line 1444 (rc2), reads:

        if ( !eZContentObjectTreeNode::showInvisibleNodes() || !$ignoreVisibility )

and the default value for $ignoreVisibility is set to FALSE when not specified in the params passed to buildSearch from ezsolr::search.

This means that

• hidden nodes will not be found, which is counter-intuitive, since they appear in the navigation
• there's no way to search for them

btw: the same behavior might apply to standard search - to be checked...