In my opinion... I wouldn't care. I suspect many other artists wouldn't either. I go to figure drawing classes.... not photography--but they are essentially related.
When drawing a nude person, the artist shouldn't care about what the model looks like. I've drawn cruvey women, buff guys, and very skinny women with large breats. Some women have extensive pubic hair--others do not.
Everyone is different. And that is the point--to grow as an artist one needs to draw and photograph many different body types. This helps the artist to over step the bounds of what is stereotypically attractive and concentate on form, movement, shape, shadows, and how nicely the drawing flows together.
If I saw a hot guy with a huge penis (8in +) who was buff and had an adorable face... I really wouldn't care. When drawing you are in a different mindset. Normally I find a naked woman's body to be "yucky," yet when I draw a nude woman, i don't thinlk about that--I can find her form to be very attractive (point: there is a difference between naked and nude).
So if a buff guy with a 3in dick was modeling for me, and then an overwiehgt guy with a 7in dick modeled for me... I wouldn't really care. I care about expressing the figure in my drawing... not what the figure happens to look like.
That is just the way I look at it. Yes in the back Iof my mind I may think, "Damn that guy is hot!" But that is where I keep it. I am there to draw and learn... not hit on the model lol. It also makes one have an appreciateion for all different body tyoes. Some people are indeed disproportional. Sometimes, that is not their fault--guys can't natuarally control their dick size. I also respect those who model who aren't "genetically gifted" "down there".. They don't care... why should i?
I'm not sure f that answers your question... or if you are specifically talking about photography for erotic books.