hudfreegamer: The answer depends on whether or not the music is included with the game or not (check the Goodies section on the game page).
Some games and soundtracks are sold separately. In that case, you can buy the soundtrack and not the game.
For example, If you want the soundtrack for Trine 2, you have to purchase that separately. If you buy the game, you won't get the soundtrack with it.
Recently though I wanted the soundtrack to an old game I used to play (Cosmo's Cosmic Adventure). The soundtrack is included with the game, so I had to buy the game to get the soundtrack.
Some game soundtracks aren't available as separate downloads or with the game. (For example, the soundtrack for Quake isn't available).
Most if not all soundtracks on Gog are treated as DLC's and you can't buy a soundtrack if you don't own the game. That is what the OP is asking.
