Yes, HALTERS is a Scrabble word!

Letter values in Scrabble US: H 4, A 1, L 1, T 1, E 1, R 1, S 1.

Is it a valid word?

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

rope or canvas headgear for a horse, with a rope for leading
a rope that is used by a hangman to execute persons who have been condemned to death by hanging
a woman's top that fastens behind the back and neck leaving the back and arms uncovered
either of the rudimentary hind wings of dipterous insects; used for maintaining equilibrium during flight

Also: hangman's rope, hangman's halter, hempen necktie.