Thanks Lukas and Sigi for your responses...
It seems even though we cannot use the FITV_POWL_APPROVER to meet the workflow requirement but we can use the generic POWL inbox "IBO_WDA_INBOX" to get workflow items in a POWL based application.
This DOC by Sagar Gadre explains in a very good way how we can have a POWL which works like a UWL and hence use NWBC for workflow related scenarios.
Closing the thread.
Regards
Sundeep