Yes, RATTERS is a Scrabble word!

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

Is it a valid word?

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

a disloyal person who betrays or deserts his cause or religion or political party or friend etc.
any of several breeds of terrier developed to catch rats

Also: rat terrier.