We are currently running PRTG Network Monitor 184.108.40.2062. This version includes a built in sensor for monitoring Dell PowerEdge Server Hardware running OpenManage on Windows, but we are looking for an all-in-one sensor that will talk directly to the iDRAC SNMP interface as it appears to provide most if not all of the same information (perhaps with a little less detail). We have converted the Dell PowerEdge R720 MIB file for iDRAC SMI v2 to an OIDLIB and confirmed with SNMPTester that we are getting data back from our iDRAC card with those OIDs.
For now, we are going to look into writing our own custom PowerShell script to query all relevant hardware information and return a good, warning, or error status depending on results, but we are probably not the only site that would find a packaged sensor helpful.
This question is related to the answer in this article which makes a note about monitoring via iDRAC: http://www.paessler.com/knowledgebase/en/topic/45333-what-do-i-need-to-monitor-dell-servers