Yes, ISOMETRIC is a Scrabble word!

Letter values in Scrabble US: I 1, S 1, O 1, M 3, E 1, T 1, R 1, I 1, C 3.

Is it a valid word?

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

related by an isometry
of or involving muscular contraction in which tension increases while length remains constant
having equal dimensions or measurements
of a crystal system characterized by three equal axes at right angles

Also: isometric line.

Not playable in Scrabble US: ISOMETRICAL.