Yes, DEADEN is a Scrabble word!

Letter values in Scrabble US: D 2, E 1, A 1, D 2, E 1, N 1.

Is it a valid word?

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

make vague or obscure or make (an image) less visible
cut a girdle around so as to kill by interrupting the circulation of water and nutrients
make vapid or deprive of spirit
lessen the momentum or velocity of
become lifeless, less lively, intense, or active; lose life, force, or vigor
make less lively, intense, or vigorous; impair in vigor, force, activity, or sensation
convert (metallic mercury) into a grey powder consisting of minute globules, as by shaking with chalk or fatty oil