Yes, NOMINAL is a Scrabble word!

Letter values in Scrabble US: N 1, O 1, M 3, I 1, N 1, A 1, L 1.

Is it a valid word?

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

relating to or constituting or bearing or giving a name
insignificantly small; a matter of form only (`tokenish' is informal)
pertaining to a noun or to a word group that functions as a noun
of, relating to, or characteristic of an amount that is not adjusted for inflation
named; bearing the name of a specific person
existing in name only

Also: noun phrase, nominal phrase.

Not playable in Scrabble US: TOKENISH.