Yes, GRINDERS is a Scrabble word!

Letter values in Scrabble US: G 2, R 1, I 1, N 1, D 2, E 1, R 1, S 1.

Is it a valid word?

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

a large sandwich made of a long crusty roll split lengthwise and filled with meats and cheese (and tomato and onion and lettuce and condiments); different names are used in different sections of the United States
grinding tooth with a broad crown; located behind the premolars
machinery that processes materials by grinding or crushing
a machine tool that polishes metal

Also: hero sandwich, cuban sandwich, italian sandwich, poor boy, submarine sandwich, milling machinery.