Yes, I reviewed a film from a training session yesterday and the only sound played was vox.
Also, when "jumping back" (moving the slider back to a certain time index) to replay sections of the film, upon hitting play it would quickly replay a compressed version of all the vox from the beginning of the film on.
Sort of the same way the film viewer replays all of the text chat from the beginning of the film when you jump back (something I also wish it didn't do), but this was with all the vox from the beginning on.