Yes, ROSTRUM is a Scrabble word!

Letter values in Scrabble US: R 1, O 1, S 1, T 1, R 1, U 1, M 3.

Is it a valid word?

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

a platform raised above the surrounding level to give prominence to the person on it
beaklike projection of the anterior part of the head of certain insects such as e.g. weevils