Yes, ONTOLOGY is a Scrabble word!

Letter values in Scrabble US: O 1, N 1, T 1, O 1, L 1, O 1, G 2, Y 4.

Is it a valid word?

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

(computer science) a rigorous and exhaustive organization of some knowledge domain that is usually hierarchical and contains all the relevant entities and their relations
the metaphysical study of the nature of being and existence