Of course you can, you can even add video
You can do it!
Any half decent DVD editing software can add a soundtrack to a video. Some would allow no video (mixed down to black), others require some video or at least an image. Play around with video editing tools, just be aware that the sampling rate of DVD audio is different from CD (48000 Hz vs 44100 hz - Someone correct me if I'm wrong please). Lastly you have more choices in audio encoding.
I use Magix Movie Edit Pro 11. Its software that people both love and hate. For example its the most feature loaded video editing software for under $100, but making a 1 hour custom DVD could take as long as 20 hours!.
Even though magix also has other sound and music editing tools (thats their strength), I actually use Movie Edit for sound editing (I'm frugal). For one You can do 5.1 positional sound, you can even use the object curve tool to create sound vectors. You can also use VST plugins to edit your sound and add effect. And finally you can write it to DVD (you'll just have to be patient)