Redshift itself doesn't use SSH.
In order to to use a SSH tunnel, Grow will need to connect to a server on the same VPC that has access to your Redshift DB. It is usually an EC2 Instance that has the PosgreSQL CLI client installed. This is because Redshift itself doesn't support SSH tunneling, but we can connect through a server that has access to the Redshift DB.
Once you have setup an additional EC2 instance inside of the same VPC, please install PostgreSQL CLI client, as well as SSH server. Make sure port #22 is open, and send us the whitelisted IP address from which we can access the server.
Questions? Email us at firstname.lastname@example.org or chat in on the site.