The primary method of creating a Facebook application is to create a page on your OWN website and then point your FB app. to load that page. When somebody or you add this application to your FB page, it automatically loads the web page that actually resides on your own web site.
Technically, you can write any code whatsoever on this web page including Google ADS. So, when this page gets displayed on Facebook, it will be able to show the ADS.
Internally Facebook