No the ratings are displayed for each Photo right on showphoto. I still dont follow you as there are no overall galleries ratings. The ratings in Photopost are for each and every photo and that has nothing to do with cats.
Creating a specific pal for this would be rather easy. If you are unable to do this you can contact me for a quote on the minor cost involved in writing that up. Send it to the email listed in my signature and specify the rating criteria if from the norm. I think currently ratings are sorted by the rating then the number of photo views.