Yes, DIGRESS is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, G 2, R 1, E 1, S 1, S 1.

Is it a valid word?

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

lose clarity or turn aside especially from the main subject of attention or course of argument in writing, thinking, or speaking
wander from a direct or straight course