The Klan had been around for decades by the time of Hitler and saw a big resurgence around the 1920's, around the same time Hitler was formulating his own racial ideologies.
Does anyone know if Hitler had ever commented on that group in any way?
I am not aware of primary sources in which Hitler mentioned the Klan. That being said, there actually was a German Klan: In 1923, Otto Strohstein, a naturalised American and Klansman, returned to Germany to found the "German Order of Fiery the Cross". That organisation had the same targets as the nazis themselves: Jews and and tteh Catholic clergy. When Nazis seized power in 1933, they immediately suppressed it.
This German Klan was not the only one in Europe, in fact there was Czech one that was opposed against Germans, Jews and "Clericals" as well as a Lithuanian one.
Sources:
Newton, Michael: White Robes and Burning Crosses: A History of the Ku Klux Klan from 1866. Jefferson, North Carolina: McFarland & Co, 2014 - ISBN 9781476617190