At the end of "Ocean's Eleven" George Clooney states a painter's name. Who is the painter and in what style does he or she paint?

I know the movie well, George Clooney makes absolutely no reference to a painter at the end of the movie. However around 35 minutes into the movie he makes 3 references regarding a painter when he is sitting having a drink with 'Tess', 2 of the references probably have no bearing on your question, he merely says "I always confuse Monet and Manet.
Which one married his mistress?"

However the 3rd reference he makes probably is the answer to your question, George Clooney says to 'Tess' "You're doing a great job at the museum.
The Vermeer is quite good."

When he says "The Vermeer" he is almost certainly referring to Johannes Vermeer's paintings. Regarding the style: Vermeer paints using a technique called pointillé.

More info - https://en.wikipedia.org/wiki/Johannes_Vermeer

Hope it helps