Yes, HEMLOCK is a Scrabble word!

Letter values in Scrabble US: H 4, E 1, M 3, L 1, O 1, C 3, K 5.

Is it a valid word?

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

poisonous drug derived from an Eurasian plant of the genus Conium
large branching biennial herb native to Eurasia and Africa and adventive in North America having large fernlike leaves and white flowers; usually found in damp habitats; all parts extremely poisonous
soft coarse splintery wood of a hemlock tree especially the western hemlock
an evergreen tree

Also: poison hemlock, poison parsley, california fern, nebraska fern, winter fern, conium maculatum, hemlock tree.