Robert, the fact that Witkin was able to bribe morgue workers does not shock me. When you take into account that minimum wage in Mexico is $150 US a month, this is no surprising. Witkin taking advantage of this is not uncommon, but as to the morality of using someones body parts to create an image which has shock value, well...let me put it this way, how would you like it if it was your aunt or brother body part? and this I think applies to any country in the world.
This to me falls in the category of shock photography, not really art but
something that creates controversy and becomes famous for that, not for the piece itself, much like Andrés Serrano's christ in piss, I had the opportunity to see the real image and it was very mediocre, but the shock value of the title and the challenging and insult to a religion was what created the controversy. I don't think is wrong to challenge the boundaries of what society considers "good taste" to create art, but when this challenge includes or is based on insult and lack of respect to create controversy I think is worthless art and I don't concern myself with it. I am sure the followers of Marilyn Manson and nine inch nails have posters of witkin's photographs, but then these are not people in society known for their good taste and respect of values. I don't think your question is really about the ethical process of creating art but the difference between freedom and libertinage. Freedom requires responsibility, libertinage is the abuse of freedom to do as we want, which in essence is what Witkin does.
As such, once the shock values has worn out the true art surfaces and we find these are not true artists. How many of you have heard of Andrés Serrano since his infamous piece? I bet very few, I had the opportunity to see his latest work and it was utterly boring and derivate. So, to me the "art" these people produce is meaningless and merely like an annoying fly which eventually will die or go away.
Well that's my two cents...for what is worth.