HFS+ mounts (readonly) fine on Linux. Read-write is not as easy, but as you're copying data from the volume you shouldn't need to worry, except of course when restoring the backup. Natch.
Forward-alashes, like any other special character (space etc.), shouldn't be a problem as long as you escape then with a backslash.
If and when you replace the NAS, probably best to pick a common filesystem for the volumes.
