I am not sure if I follow the question. The ROIs produced by SVReg are labeled both on the cortical surface as well as in the volume. The ROI based analysis will use the surface statistics, such as surface area, or it can use volumetric statistic such as volume of the ROI for comparison. It would depend on how you configured BSS when you ran the study.
The BSS module in BrainSuite can perform both surface-based and volume based analysis.
Not sure if this helps, but if not, can you please explain what you are trying to do?