seeing as how you signed a contract and what not and im assuming your getting paid, you really shouldn't use any copyright music. that being said, i would just try and find the best songs of the bunch that he keeps sending you because at least one person already approves of it.
as far as using songs that have already been used....red bull + sail = 86.9% of all of their youtube videos. and the same sports use them over and over. then think of how you react to seeing that video. if its in a super popular edit or something that lots of people have seen, i wouldn't use it. even gopro commercials on tv get old when they use electro songs aka the kayaking one with the gopro 2 and twixtor. annoys me. thats my opinion.
basically i would avoid re-using unless its from an edit some 13 yr old made and his friends are the only views