Yes, STEAMER is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, E 1, A 1, M 3, E 1, R 1.

Is it a valid word?

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

a clam that is usually steamed in the shell
a cooking utensil that can be used to cook food by steaming it
a ship powered by one or more steam engines
an edible clam with thin oval-shaped shell found in coastal regions of the United States and Europe

Also: soft-shell clam, steamer clam, long-neck clam, mya arenaria.