Yes, GRAPPLER is a Scrabble word!

Letter values in Scrabble US: G 2, R 1, A 1, P 3, P 3, L 1, E 1, R 1.

Is it a valid word?

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

combatant who tries to throw opponent to the ground
a tool consisting of several hooks for grasping and holding; often thrown with a rope

Also: grappling hook, grappling iron.

Not playable in Scrabble US: MATMAN.