@Gin:
I was surfing in the internet and i found something really interesting although I'm not sure about it's credibility an early concept of Mugiwaras by Oda in which is clearly depicted a dwarf. I would upload it but i m new here and i don't know how :p Edit: i finally made it
http://static2.wikia.nocookie.net/__cb20110710220617/onepiece/images/e/ef/Early_Crew.png
That's 100% real. It was revealed in the Green databook.
Many concepts of that original crew were mixed into what we have now. That little guy there was supposed to be the carpenter, but this idea was passed on to Franky. However, the weird guy who somehow reminds Franky was supposed to love plants (an idea that was apparently scratched away based on the current crew we have).
That image was made by Oda two years before he started the manga. The little one, however, was made just after the manga started and we can't see any dwarf in there and Chopper is now much smaller, suggesting the idea for a little guy was merged with the "reindeer" and then Chopper came to be.
Even though the ideas that would point out to a dwarf seem to be passed on to other members, I hope Oda kept the desire to have one very tiny person the group and also one who loves/work with plants (even though I don't like any dwarf that much individualy so far, I love the race).
Btw, love Chopper's first design!