Yes, GALLERY is a Scrabble word!

Letter values in Scrabble US: G 2, A 1, L 1, L 1, E 1, R 1, Y 4.

Is it a valid word?

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

spectators at a golf or tennis match
a porch along the outside of a building (sometimes partly enclosed)
a room or series of rooms where works of art are exhibited
a long usually narrow room used for some specific purpose
a covered corridor (especially one extending along the wall of a building and supported with arches or columns)
narrow recessed balcony area along an upper floor on the interior of a building; usually marked by a colonnade
a horizontal (or nearly horizontal) passageway in a mine

Also: art gallery, picture gallery.