Hi Atul,
Since Information Steward now has a lot more functionality as compared to Metadata Management 3.1, there is dependency on DS during install time and run-time. Although in your case since you only plan to use Metadata Management and Metapedia functionality of IS, DS will not be needed during runtime. Install time dependency cannot be avoided though at this time.
Note that you will not be using DS as a product in this case but it will be required only to ensure successful installation of IS.