First I would like to point out that the admin user you log into WordPress as is different than the admin user you SFTP as. Their passwords are set to be the same initially just for convenience but can be changed independently. So you could change the SFTP admin users password and share that account with people without giving them admin access to the WordPress blog. Technically however since the SFTP admin user has root access to the entire JumpBox itself so realistically they would be able to do whatever they want to the JumpBox.

So basically there is no connection between WordPress users and SSH users. Permissions on the /var/data/wordpress directory would complicate allowing other SSH users write access.

Austin