Hi,
Yes, using the MS Deploy command line is sufficient testing to verify that your package is installable using the Web Deployment Tool, which is what the Web Platform Installer and the Web Application Gallery use to install applications. If you have a Windows 2008 Server or a Windows Vista system running IIS 7.0, then you can also test with the Web Deployment Tool UI in the IIS Manager. However, we haven't added instructions for that to the documentation yet, and it is not a required step.
However, a Web application is more complex than just the installation. The Application Gallery Principles - http://learn.iis.net/page.aspx/605/web-application-gallery-principles/ - covers what is required to provide a consistent, quality user experience. The Principles cover things that testing with the Web Deployment Tool won't discover.
We look forward to receiving an application submission from you!
-Jake