DFM/OCUM has this behavior of waiting for 1 hour or 4 fsmon cycles of each 15mins before it marks the object as deleted from its database so that they are not shown in UI or cli or reports.
The mark deleted objects can still be seen if you use the switch -a with the cli like dfm volume list -a etc. In the output you will find columns named Deletedby and Deteled
and for mark deleted objects it would be dfmmonitor and YES respectively.
The reason behind 1 hour is historical due to the inital days of DFM at-least 10years back where during some monitoring cycles due to snmp errors or timeouts we dont get data from controller and dfm used to delete it from its database. Later it become false positive and reappearing in subsequent monitoring cycles.
To avoid the false positives dfm waits atleast 1 hour or 4 fsmon cycles before it declares an object is really been deleted or renamed in controller and then marks it a deleted.
Hope this explains and helps.