Yes, SERGEANTS is a Scrabble word!

Letter values in Scrabble US: S 1, E 1, R 1, G 2, E 1, A 1, N 1, T 1, S 1.

Is it a valid word?

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

any of several noncommissioned officer ranks in the Army or Air Force or Marines ranking above a corporal
a lawman with the rank of sergeant
an English barrister of the highest rank

Also: police sergeant, serjeant-at-law, sergeant-at-law.