Yes, ADMITTED is a Scrabble word!

Letter values in Scrabble US: A 1, D 2, M 3, I 1, T 1, T 1, E 1, D 2.

Is it a valid word?

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

declare to be true or admit the existence or reality or truth of
allow to enter; grant entry to
allow participation in or the right to be part of; permit to exercise the rights, functions, and responsibilities of
admit into a group or community
afford possibility
give access or entrance to
have room for; hold without crowding
serve as a means of entrance

Also: allow in, let in, take on.