"Ugly" is not a term we should use, "ugly" in one persons eyes but not in others.The "Ugly Bastard" is a stand in for the viewer AFAIK, nobody is fantasizing about fucking him, he is supposed to give hope to those of us who are average or below in appearance. To add a layer of complexity to a story as it has to explain how someone so ugly can be so successful. You are misusing the term Ugly (Ugly is by definition is unattractive!), by contrast beauty is not defined by a single template, there are arguably many ways to present it (supermodel is one of many).
There is no such thing as an "ugly" fetish because the word Ugly is purely subjective to an individuals perceptive
Besides if you'd met some of the girls I dated
You know what they say, any port in a storm.
My uncles favourite saying, "you don't look at the mantle when your poking the fire".