No. The aristocracy of europe lived off of the working class of europe. The more endogamous they were the more they would have evolved to exploit that niche more efficiently. Which means they would developed traits for parasitism. By limiting marriage between the lower classes and the elites you would be ensuring that two separate races develop eventually, with two separate behavioral traits. This is how jews differentiated from other middle easterners. They called themselves priests but the effect was the same. Parasitism, degeneracy.