Technically you wouldnt want occlusion on glass objects as such - but it all depends how you use it. In some cases a label pass and be used to clean up any unwanted occlusion, but may affect any occlusion in the background. You would only want to hide the primary visibility as the object itself could generate occlusion to a surface its contacting. Most people like to multiply their occ however using it in other ways can result in less effect on less visable surfaces - which can work well.
End of the day it is an approximated process and if you are going to render using such a method, a case by case situation is the best approach. Its the trade off for faster results.