Yes, HADDOCK is a Scrabble word!

Letter values in Scrabble US: H 4, A 1, D 2, D 2, O 1, C 3, K 5.

Is it a valid word?

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

lean white flesh of fish similar to but smaller than cod; usually baked or poached or as fillets sauteed or fried
important food fish on both sides of the Atlantic; related to cod but usually smaller

Also: melanogrammus aeglefinus.