http://www.usmagazine.com/celebrity-news/news/leonardo-dicaprio-to-testify-in-wolf-of-wall-street-lawsuit-w210541
Admittedly, I don't know the full facts, but at first sight it appears to me to be a money grabbing vexatious lawsuit. It's not beyond the bounds of possibility that Andrew Greene sees himself in the character Nicky "Rugrat" Koskof, and dislikes what he saw. However, as far as I can tell, Greene was not mentioned in the script in any contentious, nor defamatory way. Moreover, most films, and I'd guess this one too have clauses on the credits disclaiming that the characters represent actual people, either alive or dead. With that in mind, it seems highly unlikely that any rational jury will find that the film was calculated to damage his reputation to third parties. Just my take on the article... you may see things differently.
http://thelawdictionary.org/article/how-do-you-prove-a-defamation-of-character-claim/
I read about this in the Wall St. Journal. Generally, it is hard to prove defamation of character in the USA if you are a public figure or if the character is a composite of multiple people. I don't think the movie makers have much to worry about.