Yes, BRIDGEHEAD is a Scrabble word!

Letter values in Scrabble US: B 3, R 1, I 1, D 2, G 2, E 1, H 4, E 1, A 1, D 2.

Is it a valid word?

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

an area in hostile territory that has been captured and is held awaiting further troops and supplies
a defensive post at the end of a bridge nearest to the enemy