Yes, FRATERNIZE is a Scrabble word!

Letter values in Scrabble US: F 4, R 1, A 1, T 1, E 1, R 1, N 1, I 1, Z 10, E 1.

Is it a valid word?

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

be on friendly terms with someone, as if with a brother, especially with an enemy

Not playable in Scrabble US: FRATERNISE.