Yes, MAMEY is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, M 3, E 1, Y 4.

Is it a valid word?

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

tropical American tree having edible fruit with a leathery rind
globular or ovoid tropical fruit with thick russet leathery rind and juicy yellow or reddish flesh

Also: mammee apple, mammee tree, mammea americana.