Yes, POLYMORPHOUS is a Scrabble word!

Letter values in Scrabble US: P 3, O 1, L 1, Y 4, M 3, O 1, R 1, P 3, H 4, O 1, U 1, S 1.

Is it a valid word?

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

relating to the crystallization of a compound in two or more different forms
relating to the occurrence of more than one kind of individual (independent of sexual differences) in an interbreeding population
having or occurring in several distinct forms