Yes, ROCKET is a Scrabble word!

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

Is it a valid word?

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

any vehicle self-propelled by a rocket engine
a jet engine containing its own propellant and driven by reaction propulsion
erect European annual often grown as a salad crop to be harvested when young and tender
propels bright light high in the sky, or used to propel a lifesaving line or harpoon
sends a firework display high into the sky

Also: rocket engine, garden rocket, rocket salad, eruca sativa, eruca vesicaria sativa.