Ensembles has had support for Dropbox as a backend since the very beginning, but it was based on the Dropbox Core SDK, which is a thin wrapper around their REST API.
Ensembles 2 now includes support for a backend based on the Dropbox Sync API. This is more recent to Dropbox's developer offerings, and includes local caching. The new backend has been added to the master branch on GitHub, and will be in the next release of Ensembles 2.
Ensembles 2 can be purchased here, including packages with full source code.