ssh should be available. Not sure on which version of AIX (5.2?) it became standard. You will have to generate a private and public key without entering a password when being asked at creation (ssh-keygen) for the user. They will be place under ~/.ssh. To have passwordless authentication you will have to add the pub-key of the "client" to the authorized_keys file of the remote host to grant access.
There should be some posts here in the forum or on the web how to set it up step by step.