Yes, BIOHAZARD is a Scrabble word!

Letter values in Scrabble US: B 3, I 1, O 1, H 4, A 1, Z 10, A 1, R 1, D 2.

Is it a valid word?

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

hazard to humans or the environment resulting from biological agents or conditions
any bacterium or virus or toxin that could be used in biological warfare

Also: biological agent.