Yes, PITAHAYA is a Scrabble word!

Letter values in Scrabble US: P 3, I 1, T 1, A 1, H 4, A 1, Y 4, A 1.

Is it a valid word?

PITAHAYA is a valid word in the official Scrabble dictionary (US) and the UK Scrabble Dictionary, but not in Words with Friends (ENABLE).

cactus of the southwestern United States and northern Mexico having edible juicy fruit
highly colored edible fruit of pitahaya cactus having bright red juice; often as large as a peach

Also: pitahaya cactus, acanthocereus tetragonus, acanthocereus pentagonus.