Yes, ROCKER is a Scrabble word!

Letter values in Scrabble US: R 1, O 1, C 3, K 5, E 1, R 1.

Is it a valid word?

ROCKER is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

an attendant who rocks a child in a cradle
a performer or composer or fan of rock music
a teenager or young adult in the 1960s who wore leather jackets and rode motorcycles
a chair mounted on rockers
a trough that can be rocked back and forth; used by gold miners to shake auriferous earth in water in order to separate the gold
an ice skate with a curved blade
a curved support that permits the supported object to rock to and fro

Also: rock 'n' roll musician, rocking chair.