Yes, NONSYLLABIC is a Scrabble word!

Letter values in Scrabble US: N 1, O 1, N 1, S 1, Y 4, L 1, L 1, A 1, B 3, I 1, C 3.

Is it a valid word?

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

not forming a syllable or the nucleus of a syllable; consisting of a consonant sound accompanied in the same syllable by a vowel sound or consisting of a vowel sound dominated by other vowel sounds in a syllable (as the second vowel in a falling diphthong)
(of speech sounds) not forming or capable of forming the nucleus of a syllable

Not playable in Scrabble US: UNSYLLABIC.