Yes, INFERENTIAL is a Scrabble word!

Letter values in Scrabble US: I 1, N 1, F 4, E 1, R 1, E 1, N 1, T 1, I 1, A 1, L 1.

Is it a valid word?

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

relating to or having the nature of illation or inference
of reasoning; proceeding from general premisses to a necessary and specific conclusion
resembling or dependent on or arrived at by inference
derived or capable of being derived by inference
based on interpretation; not directly expressed