I have a variety of OpenManage versions that have this issue (ranging from 5.5 to 6.3). From time to time, either because of Windows Update or just after a week or so, servers will drop from the Dell Servers state view in the management pack. The only solution I have come up with so far involves running a batch file on the affected servers. I cannot keep the servers from dropping from the management pack, but at least I have a reasonably quick way of correcting it.
Place the server in maintenance mode under Windows Computers (NOT Dell Servers) and use the following commands in an elevated command prompt:
net stop HealthService
net stop dcstor32
net stop "Server Administrator"
net stop dcevt32
net stop omsad
net start omsad
net start dcevt32
net start "Server Administrator"
net start dcstor32
net start HealthService
The dcstor32 service takes quite a long time to stop and start again, but it always works. Once the machine comes out of maintenance mode (either set it for 5 minutes or just stop maintenance mode a minute or so after HealthService starts), then for the next 2 minutes all of the Dell manangement pack discoveries complete and show their state in the state view.
The management pack is extremely helpful in getting alerts to admins when a drive fails or when one power supply of the two loses power, but this problem of them dropping out is somewhat annoying. From what I can gather, this has to do with WMI on the affected servers and not SCOM itself. If there is a better solution involving reregistering something, I would be open to try it. In our environment, we only have 21 Dell servers to monitor, so each day I look at the list in the state view and see if we lost one. I'm not quite sure if there's a way to alert when a server loses the Dell Server class, but if it were possible, scripting this batch file would become amazingly effective in keeping servers in the list. Also, this works if a server is still listed and, for some reason, loses one of the state views, such as Storage or Memory.