You can use OS or Oracle authentication. If you are using Oracle authentication, you could have a 'service' account created that has the necessary roles/permissions to run the backups.
If you use 'Unix OS credentials', again you could have a 'service' account created. Also, if you are going to 'Use Oracle RMAN recovery catalog', you would need the rman account information.
Did you have a DBA create the account called 'sys' for you on that instance? Otherwise, that account won't work because it doesn't exist.
You also need the OS credentials too, doesn't have to be root, it can be a service account.
OS Credentials if for access to the server, Oracle Authentication is for access to the DB, two seperate things.
Here is an instance group.