Update: Still having the same problem. Open ticket with Dell Tech support, and still no resolution. I can "temporarily" get the systems to respond by doing a manual "refresh inventory" and "refresh status " but the server will (with 24 hours) go back to an "Unknown" health status.
Discovery is every day at 1AM
Inventory is every day at 2AM
Status is every hour, polling speed "slow"
Running the troubleshooting tool gets good response to both ICMP and SNMP, even when server health is "unknown".