I think you need host ID, not the host name. Did you try that? What command did you use?  In my case, RP is Hots_266  service@(none) spa:~> uemcli /remote/host show ... 4:    ID              = Host_266  <<<<<<<<<<<<<<<       Name            = RecoverPoint       Description    =       Tenant          =       Type            = rpa       Address        =       Netmask        =       OS type        = RecoverPoint       Ignored address =       Health state    = OK (5)       Health details  = "The component is operating normally. No action is required."   And then just had the LUN to host (I am using LUN id sv_657 as an example here):  08:40:01 service@(none) spa:~> uemcli -u admin -p yourpassword /stor/prov/luns/lun -id sv_657 set -lunHosts Host_266  ID = sv_657 Operation completed successfully.
I have about 150 Recoverpoint Journals that have already been created on a Unity 400F.  If I try to add the recoverpoint host via command line to all of the luns, i get an error.  Operation failed. Error code: 0x6401060  The value specified for the '-lunHosts' qualifier is invalid: RecoverPoint OBSOLETE. 
Unable to add -lunHosts RecoverPoint to Recoverpoint Journal Volumes on 400F