Unfortunately, on an MS switch there is not currently a way to explicitly view the ports with known group members based on the snooped IGMP messages. Being able to check this could for sure come in handy -- I have passed along a feature request.
Thanks Andrew that brings up another Q about enhancement requests. (ER) Is there a ref number assigned to a ER that I could look up time to time? Can I open ERs already made so I am not duplicating or perhaps can agree with one already made?