Yes, MESCAL is a Scrabble word!

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

Is it a valid word?

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

a small spineless globe-shaped cactus; source of mescal buttons
a colorless Mexican liquor distilled from fermented juices of certain desert plants of the genus Agavaceae (especially the century plant)

Also: lophophora williamsii.