I have some experimental code for VST UIs in Linux (using openGL), it's not ready for release...
I've uploaded a source tarball with a plugin inside, although the UI seems to have some little issues right now:
http://kxstudio.sourceforge.net/tmp/3BandEQ-VstTest1.tar.gzI'll work more on it soon, so for now it can be a "preview" of how it is done.
But in short, it uses something I call "DISTRHO Plugin Toolkit", which similar to Juce can make a single source code compile into different plugin APIs (At the moment LADSPA, DSSI, LV2, VST and Standalone, some better than others).
This plugin uses openGL for the UI, but Qt4 can be used alternatively.
Again, this is very new stuff, not ready for release!