Yes, STOCKADE is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, O 1, C 3, K 5, A 1, D 2, E 1.

Is it a valid word?

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

fortification consisting of a fence made of a line of stout posts set firmly for defense
a penal camp where political prisoners or prisoners of war are confined (usually under harsh conditions)

Also: concentration camp.