The CV outs on the Theremax were my initial attraction to the Theremin. When I built my Theremax in September of 2005 I assumed that I would never be able to play the Theremin but gestural control would be a nice way to add some nuanced expression to my analog synthesizer.
However, things changed when I started to play the Theremin and I have tended to use the Theremin in a stand-alone manner.
There are probably many people who utilize the CV outs -- however, depending on the processing involved, the result may not be identifiable as a Theremin.
When thinking about "who uses CV outs" a few people come to mind --
Barbara Buchholz and Lydia Kavina did a program entitled "Touch, Don't Touch" wherein they use Theremins to trigger samples.
Wilco Botermans processes his theremin through effects and some of the sounds that he creates could be done with CV outs (though, I am not sure exactly how he does it.)
Check out Anthony Ptak, too. He does some excellent electronic music that is gestural-controlled.
At times I wish I had some switches and/or pots that were panel mounted that could be used to control peripherals. Wouldn't necessarily need the effects in the theremin's cabinet. Would be nice to have controls within easy reach.