Yes, REPEATERS is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, P 3, E 1, A 1, T 1, E 1, R 1, S 1.

Is it a valid word?

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

a person who repeats
someone who is repeatedly arrested for criminal behavior (especially for the same criminal behavior)
a firearm that can fire several rounds without reloading
(electronics) electronic device that amplifies a signal before transmitting it again

Also: habitual criminal, repeating firearm.