The VideoLAN Forums

Fedora 8 features the PulseAudio Volume Control, which acts as a mixer, and allows for each individual application's output volume to be adjusted.

When the "vlc" volume slider in the PulseAudio Playback tab changes, the corresponding slider in VLC should also change, rather than having two output stages.

Well, No.
you have to write a PulseAudio Output module for that to work.

Yes, yes, yet another audio server...