Hi Amy
We've just been doing exactly this with one of our courses.
The front end & JavaScript developers work on a local copy of the framework that they download via our version control system (Subversion).
When they have completed working on their component/extension/theme/menu they then commit their changes to the version control system and then upload what they were working on into the Authoring Tool.
(Note that if you are updating a plugin that has already been uploaded to the Authoring Tool, it is necessary to increment the version number in bower.json i.e. from 1.0.0 to 1.0.1)
We also regularly exported the content from the authoring tool into version control so that if the developers needed to fix bugs/make further changes they would have an up-to-date copy of the course content to work against.
In theory if your developers had file access to the server running the authoring tool then you might be able to do something a bit smarter, at the very least you'd be able to simply overwrite the plugins directly rather than having to upload (unless you need to make changes to the plugin's properties.schema in which case you still have to upload)
Hope this helps