It depends on what you're trying to accomplish. Are you going to just be reading the server data, or are you planning on editing the world on another system and having it update?
If the latter, you're out of luck (unless you want to do some in-depth management, and even then Minecraft might keep copies of chunks in RAM and overwrite your updated version).
If you just want to be able to copy the files elsewhere, the easiest way may be to write a simple cronjob to automatically copy your Minecraft data every ten minutes or so:
*/10 * * * * cp -r /home/user/.minecraft /your/dropbox/folder/
You may end up wanting to tweak the 10-minute timer though, maybe to 15 or higher depending on how tolerant Dropbox is of your Minecraft shenanigans.
The other option is, as stated, to make a symbolic link:
ln -s ~/.minecraft/ /your/dropbox/folder/
...but as was stated above, this is a bad idea for a whole bunch of reasons.