Yes, even though the server doesn't play the sound, it still needs it in order to handle it properly. Kind of like models. If you try and play a sound file that doesn't exist, it will not play. In the case of soundscapes it'll play a default.
Take a look at the sound files being used inside of your manifest files and simply upload those to your server, maintaining folder structure (etc etc).
You may need to extract them from the game's vcd file. You can use
GCFScape to do this.
