Wetherbee,
After some investigation it seems the lack of results coming back from identifying have something to do with the Spatial references in this scenario. The webmap is in Web Mercator (102100), and the Map Service is in wkid 2007.
I will continue to follow this up - but it seems you can workaround this if the Spatial References are consistent. Either both are in 102100, or both are in 2007, I am seeing the identify return results in Explorer.
Can you try using a Basemap layer that is in 2007 (so that the webmaps SR will be wkid 2007)? and see if you now get the identify results?
In general, this should not be a problem for these to be different - but this case seems to be causing an issue. I'm looking into the possibility that a Datum transformation (or lack thereof) might be at play here. I will follow up discussions with others who know more about this specific aspect and get back to you.
Best,
Heather