you are asking an interesting question and perhaps you need to elaborate on your definition of a distributed version control system just to ensure that I am answering the right question. Bitbucket of course is essentially a wrapper around Git which itself is a distributed version control soluton (VCS).
That does not necessarily mean that you have use it that way. I support Bitbucket in an enterprise environment as I have with IBM's RTC and ClearCase. It is distributed in that we clone repos, which can actually be used as distributed master repos (e.g. bare repo). ClearCase was certainly a server model but you could use it with snapshot views. Subversion and RTC both allowed you to create sandboxes or workspaces which have many properties similar to cloning a repo.
So the simple answer to your question is that Bitbucket is a wrapper around Git which is a distributed VCS. But we could discuss your use case a little more - which might more closely resemble a server model
Bob Aiello, Technical Editor