Unfortunately the lack of Refresh Hardware events in this case does mean a problem in gathering data from vCenter.
This is one of the reasons that we do not claim vSphere 5 support for nworks 5.6 - only our up-coming 5.7 release fully and natively supports vSphere 5 API in all departments.
However the good news is that our 5.7 release is VERY close - it is difficult to promise exact dates, even this close - but we are in final QA, and the release date is days not weeks away.
We do have a Release Candidate build of the 5.7 MP available, if you would like to install that and restore your monitoring - alternatively, the actual release is so close you may prefer to wait for the GA code.
Any queries on the above please let me know,
Vice President, Product Management