netbackup unable to resolve hostname <hostname>, no hostname alias added to pem name manager.

Now there's about 16 of these servers and they have all been decommissioned and they are not associated with any policy and they are not under client's host properties on the GUI. Upon searching under the /usr/openv/netbackup/db/client directory, all 16 of these client folders are still in there. Is it OK to just remove/delete these client folders on this directory? Or is there another way of getting rid of these error?