Deja Dup is just a front-end (and configuration helper) for Duplicity. From its --help, you can see what it supports:
cf+http://container_name
file:///some_dir
ftp://user[:password]@other.host[:port]/some_dir
ftps://user[:password]@other.host[:port]/some_dir
hsi://user[:password]@other.host[:port]/some_dir
imap://user[:password]@other.host[:port]/some_dir
rsync://user[:password]@other.host[:port]::/module/some_dir
rsync://user[:password]@other.host[:port]/relative_path
rsync://user[:password]@other.host[:port]//absolute_path
s3://other.host/bucket_name[/prefix]
s3+http://bucket_name[/prefix]
scp://user[:password]@other.host[:port]/some_dir
ssh://user[:password]@other.host[:port]/some_dir
swift://container_name
tahoe://alias/directory
webdav://user[:password]@other.host/some_dir
webdavs://user[:password]@other.host/some_dir
gdocs://user[:password]@other.host/some_dir
mega://user[:password]@other.host/some_dir
dpbx:///some_dir
And as you can see, both Mega and Dropbox are both on the end of that list. I would expect most of those to be available through Deja Dup.
Note: This appears to be new in Trusty. So you would either need to upgrade (pre-release at the time of writing) or manually suck the duplicity package back from packages.ubuntu.com. If you do the second, just check you can fulfill all the dependencies from your Ubuntu version before you upgrade. If you can't and you install anyway, that can cause a bit of a headache.