Hi Jaya,
The rights it looks for include Resource - Soft book and Resource - View. At a minimum they would need Resource - View, but if you grant Resource - Soft book, this also enables them to see the resources in the portlet. If the access is granted at the global level, then all users would see the same amount of resources in the results, but if it's granted at the OBS or Instance level, then they would then potentially see varying results depending on whether the users are granted access to the same OBSs or resources (at the instance level).
Regards,
Kristin Schroer