That's correct. The SQL Packager command line doesn't have the functionality to deploy directly from source control. It's not just that it's hidden, it's actually using an older SQL Compare engine that doesn't have that functionality.
If you have the API for SQL Packager, i.e. the SQL Comparison SDK
, then you can also use the SQL Compare API, but I think you're referring to the command line interface to SQL Packager not the API.
If you want to automate the deployment of a schema directly from source control, you will need to use SQL Compare command line or the SQL Compare API.
I hope this helps clear things up.