Is it possible to connect a single Dropbox Mac app with two or more Dropbox accounts?
You can't do it out of one copy of the app, but it seems that you can duplicate the app. You can see (somewhat complicated) instructions here:

http://maketecheasier.com/run-multiple-dropbox-accounts-in-mac-and-linux/2010/05/24

I haven't done this personally, but this looks like it should work.