Yes, SHELLACS is a Scrabble word!

Letter values in Scrabble US: S 1, H 4, E 1, L 1, L 1, A 1, C 3, S 1.

Is it a valid word?

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

lac purified by heating and filtering; usually in thin orange or yellow flakes but sometimes bleached white
a thin varnish made by dissolving lac in ethanol; used to finish wood

Also: shellac varnish.