Yes, NAZI is a Scrabble word!

Letter values in Scrabble US: N 1, A 1, Z 10, I 1.

Is it a valid word?

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

a German member of Adolf Hitler's political party
derogatory term for a person who is fanatically dedicated to, or seeks to control, some activity, practice, etc.

relating to or consistent with or typical of the ideology and practice of Nazism or the Nazis
relating to a form of socialism

Also: german nazi, national socialist.