If you import the task as zipped job the commandline does not build the task again (it simply creates the task entry and manage the deployment). The libraries under lib/java will automatically synchronized via SVN. To do that the SVN settings in the TAC contains settings for a repository dedicated to the libraries.
The commandline automatically synchronise it self via this SVN repo. You do nota have to do anything on it.
If you start the very first studio in your environment it suggests to download a lot of Modules (actually libraries or jars) and all of them will automatically committed to SVN. All other studios update their lib/java dir from SVN also the same procedure in the commandline (which is actually nothing else then a studio).