Gotta pause you there, Prince. 

Marrow's character IS Main House, for one. For two, 64/128/Vacuum Palm aren't Hiden in any way. Rather more advanced applications of Gentle Fist that are kept out of the hands of the Branch House. Though I will agree that it would be hard even for a 15 year old Main House Genin to learn the 64-Palms. That move is REALLY potent.