Yes, HOLISMS is a Scrabble word!

Letter values in Scrabble US: H 4, O 1, L 1, I 1, S 1, M 3, S 1.

Is it a valid word?

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

the theory that the parts of any whole cannot exist and cannot be understood except in their relation to the whole

Also: holistic theory.