Yes, the roll is taken into account. The separation is applied after the head transformation.
Symmetric viewing is enabled for HMDs and asymmetric viewing is enabled for powerwall/CAVE setups. Take a look at the following pages for more information:
http://docs.worldviz.com/vizard/Intr...o_displays.htm
http://docs.worldviz.com/vizard/Stereo_rendering.htm