Yes, HALIBUT is a Scrabble word!

Letter values in Scrabble US: H 4, A 1, L 1, I 1, B 3, U 1, T 1.

Is it a valid word?

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

lean flesh of very large flatfish of Atlantic or Pacific
marine food fish of the northern Atlantic or northern Pacific; the largest flatfish and one of the largest teleost fishes