The function is based on the inclusion of the _spotlight user in the ACL table for the share. And the permissions must be propagated. Follow these general steps:
1: In Server Admin, click on the Sharing tab
2: Select your Share point from the list and then press the Share Point tab view
3: Make sure the "Enable Spotlight searching" check box is selected.
4: Now go to the Permissions tab (right next to Share Point)
5: You will notice that a new ACE exists in the ACL table (_spotlight)
6: On the bottom of the Permissions pane, click the gear popup menu and select Propagate Permissions
7: By default, the "access Control List" is checked. That is usually all it needs.
8: Press OK
Now, depending on how much data you have, this may take some time to index. On the server, what the Spotlight magnifying glass in the top right corner. A small black dot will appear in the center of the magnifying glass. Wait until this goes away. Then unmount and remount the share on your clients. That should do it.
Hope this helps