Yes, WORKER is a Scrabble word!

Letter values in Scrabble US: W 4, O 1, R 1, K 5, E 1, R 1.

Is it a valid word?

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

a person who works at a specific occupation
a member of the working class (not necessarily employed)
sterile member of a colony of social insects that forages for food and cares for the larvae
a person who acts and gets things done