That's a good question, and one I've asked myself, even though I don't have a mac (yeah, I'm odd).
Firstly, assuming your Dreambox has an HDD, I cannot think of any reason why not, as the network link is simply using the TCP-IP protocol.
As long as your FTP client can read the file system (whichever one you formatted it with, there is a choice) on the Dreambox (linux) box - via its FTP server, then I can't see a problem.
If you have no HDD, then I'm even more confident - but still wouldn't bet my house on it!
STICK
P.S. Thanks Rolf, you beat me to it again!!!