Yes, SQUATTERS is a Scrabble word!

Letter values in Scrabble US: S 1, Q 10, U 1, A 1, T 1, T 1, E 1, R 1, S 1.

Is it a valid word?

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

someone who settles lawfully on government land with the intent to acquire title to it
someone who settles on land without right or title