First make sure the key generated form PuttyGen is type SSH-2 RSA or SSH-2 DSA. The SSH-1 RSA is not supported.
Copy and paste the public key somewhere, you'll need it on the target RedHat server. Add the string to the .ssh/authroized_keys file of the desired user's home directory.
Export the private key from PuttyGen with the Conversions menu -> "Export OpenSSH Key"
Place this file on the RAS. For the privateKeyFile input, specify the path to this file. User's username is still required. When a privateKeyFile is specified, the password input becomes the passphrase input for the private key file. If no passphrase was specified for the key file, anything can be used in the input.
I was having the same issue running HPOO 10.22. The solution was installing PPK file on the Central server. Works fine. However, what I'm still unable to get working is using a passphrase with key. I read that the passphrase is entered in the password field if you have key specified but I cannot get key authentication to work with a passphrase.