Ratings are on a per photo basis. So if 30 users rate the photo the rating changes with it.
You can write a short script pal box to poll the results just in one category of Photo's to display the top rated highest to lowest.
So I dont see where your going with saying ratings are messed up when you have other categories.
As far as the license question you may not have two installs per license even if they share one database. License states one install per domain per license.