Board Thread:Antaeus' Arena: Audience Chamber/@comment-1515612-20160831210117/@comment-29154221-20160905144209

''"Hazel used her abilities to levitate some items from the bottom of the sea." -The Son of Neptune ''

So unless Percy is blind and/or stupid, I'm pretty sure he would notice shiny gold weapons levitating in the water. So yes, Percy knows that Hazel can control metals.