Does the passthrough 30-pin port also work for music playback?

Would compatible accessories, e.g. docks, be able to play audio by connecting to the 30-pin port (the one that is meant for charging)?
I know HDMI transfers sound, but I would rather do it this way.

Apple 30-pin Digital AV Adapter

Apple 30-pin Digital AV Adapter

Product No Longer Available

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