Yes and no. It can crawl documents on an NFS volume, but the sharepoint database or logs cannot be stored there.
How is SharePoint Portal Server different from the Site Server?
Site Server has search capabilities but these are more advanced using SharePoint. SPS uses digital dashboard technology which provides a nice interface for creating web parts and showing them on dashboards (pages). SS doesn't have anything as advanced as that. The biggest difference would be SPS document management features which also integrate with web folders and MS Office.