By default Aptana is configured to work with its own Git implementation meaning that whenever you add a Git repository and import it to the workspace, the default Aptana Git functionality is available in the project. The problem is, it doesn't always deliver, e.g. for GitHub, nor is it visually as complete and readable.
The alternative is the more comprehensive eGit plugin for Eclipse. To switch over to eGit, just tick off Preferences > Team > Git > Automatically attach our git support to projects added that have git repositories.
This feature landed in Aptana Studio 3 roughly a year ago, see Preference for git - egit integration.