Yes, GRATINGS is a Scrabble word!

Letter values in Scrabble US: G 2, R 1, A 1, T 1, I 1, N 1, G 2, S 1.

Is it a valid word?

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

a barrier that has parallel or crossed bars blocking a passage but admitting air
a frame of iron bars to hold a fire
optical device consisting of a surface with many parallel grooves in it; disperses a beam of light (or other electromagnetic radiation) into its wavelengths to produce its spectrum

furnish with a grate
gnaw into; make resentful or angry
reduce to small shreds or pulverize by rubbing against a rough or sharp perforated surface
make a grating or grinding sound by rubbing together
scratch repeatedly

Also: diffraction grating, eat into.