Interesting experiment there with some actual numbers. http://blog.eat24hours.com/how-to-advertise-on-a-porn-website/
"The evidence was in. Porn advertising is an untapped market, and our mission was clear: Tap. Dat. Ass." Hilarious!! Thx for the link.
The golden age of porn ended in 2000, the second one in 2008-2009, now its peanuts compared to the money it was making before. I mean for regular affilates and website owners.
That is a good case study. But you really need to convince your client to put some ads on that site. Because It can damage a brand if you do it wrong.