My understanding is that restricted pages are currently searchable by users who have access to the restricted pages, but not site-admins (confluence-administrators group). Though confluence-administrators DO have access to the restricted pages if they access the restricted page directly. Can this be adjusted so confluence-administrators also have access to the portion of the search index which contains restricted pages?

One use case is for lite e-Discovery (something Confluence does not provide natively). If a Confluence site has a large number of restricted pages, it is practically impossible for an authorized account to search for content relevant to an e-Discovery search.