You may be over-thinking this. In the UserList file, you can add a specific hostname in the 4th field (the * without the " marks, for example
"*" "*" "*" mysys.hp.com "admin"
If this does not connect, we are probably looking at a hostname resolution issue. If it does connect, you can restrict access even more by putting a username in the 2nd filed, for example
"*" "MSC12" "*" mysys.hp.com "admin"
This can also be done from the GUI, I just find it easier to edit the file
Keep in mind that if the 'hostname' is a Windows system, the username must be in upper-case characters