Yes, PEACEKEEPER is a Scrabble word!

Letter values in Scrabble US: P 3, E 1, A 1, C 3, E 1, K 5, E 1, E 1, P 3, E 1, R 1.

Is it a valid word?

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

a member of a military force that is assigned (often with international sanction) to preserve peace in a trouble area
someone who keeps peace
the pistol of a law officer in the old West