I've checked the dfmmonitor logs and here what I see:
May 14 15:26:44 [DFMMonitor:ERROR]: [1068:0x1580]: Error in INSERT INTO disks ( DiskName, DiskRPM, DiskId, DiskPort, DiskTotalBlocks, DiskAdapter, DiskUsedMB, DiskBay, DiskVolume, DiskSecondaryDiskPort, hostId, DiskShelf, DiskModel, DiskScsiId, DiskGroup, DiskTotalMB, DiskStatus, DiskType, DiskDiskNumber, diskRole, DiskSecondaryDiskName, DiskGroupNumber, DiskUsedBlocks, DiskCompletionPerCent, diskUniqueId) VALUES ( 'data disk 2d.10.7', '15000', '7274497', '1', '-822052480', '2d', '1695446', '7', '1', '2', '75', '10', 'ST2000NM0011SM', '121', '1', '1695759', '1', 'BSAS', '11', 'data', '2a.10.7', '1', '-822693376', '0', 2194): (-158) [Sybase][ODBC Driver][SQL Anywhere]Value '-822052480' out of range for destination
May 14 15:26:44 [DFMMonitor:ERROR]: [1068:0x1580]: Error inserting disk data disk 2d.10.7for host filer_name (75)[Sybase][ODBC Driver][SQL Anywhere]Value '-822052480' out of range for destination
My guess is that that Operations Manager 4.0 doesn't support large disks. It's 1.6TB SAS drives and given that aggregates with smaller drives show up just fine it's a dumb overflow issue for DiskTotalBlocks and DiskUsedBlocks fields.
Can somebody confirm my findings?