rsync already defaults to ssh as transport but with $ rsync -e 'ssh -i keyfile' you can use rsync with a ssh key.
Yes, that was what I had been doing, but I wanted to avoid the use of ssh completely, the connection is secured over a vpn, silly to incur the overhead of encryption, twice.
An rsync daemon was used and the passwords automated with a password file and this has been working well for a few days...