Yes, GRAMPUS is a Scrabble word!

Letter values in Scrabble US: G 2, R 1, A 1, M 3, P 3, U 1, S 1.

Is it a valid word?

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

predatory black-and-white toothed whale with large dorsal fin; common in cold seas
slaty-grey blunt-nosed dolphin common in northern seas

Also: killer whale, sea wolf, orcinus orca, grampus griseus.