There no necessary need for that, I'll advice you to focus more on bounties hosted by reputable platforms or quality campaign manager that will ensure it's particpant gets the best from any bounty the take part in. This will be a better approach than having a Bounty rating website, as we should be aware they'll likely be manipulating the ratings.
Well, or the easiest option is to track projects that appear on our forum. And after an in-depth analysis of the projects, take part in the selected company.