"natural bodybuilding" is an oxymoron for many reasons.
Powdered Creatine itself is not "natural". It's a synthetic concentrated powder of the amino acids produced in a factory,It's anything but "natural". It occuring naturally in the body or existing in foods doesn't mean concentrating it into a powder makes it natural.
The word "natural" comes from the latin word
naturalis meaning "From birth" in that sense the second anyone is born they are no longer "natural" but are changed due to "Society".
If you consider synthetic concentrated powdered creatine "Natural" then you must also consider synthetic testosterone "natural". Both occur naturally in the body, Both were synthesized and concentrated in a lab, Both are taken to increase the natural levels of the chemicals in the body. Nothing about synthetic powdered creatine concentrate makes it more natural than synthetic testosterone injections.
Nothing about Bodybuilding is "natural". Lifting weights molded from steel over and over daily is anything but "natural". You'll never find such equipiment in nature. Consuming thousands of calories a day is not "natural" espically 200grams of protein.
There's such a thing as "nature" and "Nurture". Having 14 inch arms that nature intended is "natural"..Building them to 18 inches by lifting weights for 10 years is "nurture" and is no longer considered "natural" but environmental.
Here is an article by Rick Collins I highly recomend.
"Natural Bodybuilding" - Modern Oxymoron?
http://www.mesomorphosis.com/articles/collins/natural-bodybuilding.htm