Yes! You can use Stratus for on-demand coauthoring, while using Dropbox (or any other cloud storage provider) for long-term storage.
For example, if you store all of your team’s files on Dropbox, you may still find that it’s useful to have access to coauthoring when preparing for a debate, or when working with a teammate in a different location, without needing to deal with email or conflicted copies. You can just upload the document you want to work on to Stratus, coauthor it with them, and then download the completed version to Dropbox to re-integrate with your files later. Or, store your files on Dropbox, but use Stratus for storing speech documents.
Alternately, you can just use Stratus for all your file storage needs, and take advantage of advanced features like version control.