Yes, STUFFER is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, U 1, F 4, F 4, E 1, R 1.

Is it a valid word?

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

a craftsman who stuffs and mounts the skins of animals for display
an advertising circular that is enclosed with other material and (usually) sent by mail

Also: animal stuffer.