Real vanilla extract in vanilla vodka?
Well, real vanilla extract is basically alcohol, into which vanilla beans have been added. Alcohol is a solvent and is extractive of certain flavors. With regards to commercial brands of vanilla flavored vodka, I guess it would depend on the producer. Regional/artisan distillers are more likely to flavor their vodkas with real ingredients, whereas commercial brands like absolut are probably more likely to use imitation flavoring.
That said, making flavored vodka is one of the easiest things in the world to make at home, and gives you much more control of the final product. Just put some vanilla beans into a mason jar, fill with your favorite vodka, and let it steep. Taste it every so often; once you've gotten it where you like it, just strain out the solids and rebottle.