I never succeed in installing it fully silently.
On a machine install the soft manually ==> will create c:\Program files\radmin.
Configure it manually as you want, with filters, security, ....
After that, if you copy the files (I think that min 3 are necessary : raddrv.dll, admdll.dll and r_server.exe )in a directory and then start r_server /installservice and finally you will receive a popup that service is installed. After start the service with
net start "Remote Administrator service"
and apply the registry key exported from the manual installation (HKLM\system\Radmin). It should be ok.
If registration doesn't go, you have 30 days to connect on the machine and type registration key manually. With version 2.1 you can remotely apply the licence. With version before 2.1, you don't need to apply licence and it seems to go when you made only copy of files (no full setup).
I never received informations form silent setup.