Hi Atul
The use of the Portal-independent navigation frame on the sell side is not recommended, as SAP NetWeaver Business Client (NWBC) does not support branding and cascading stylesheets (CSS).
You can only use SAP NetWeaver Portal on the sell side when you deploy SAP Supplier Lifecycle Management with supplier self-services.
So yes buyside you may use NWBC but sell side it is recommended to use Portal.
Read more about navigation below
Navigation Frames - SAP Supplier Lifecycle Management - SAP Library
To register supplier you need to activate a business function read more here:
Registering As a Supplier - SAP Supplier Lifecycle Management - SAP Library
Regards
Vinita