Yes, MULTIVALENT is a Scrabble word!

Letter values in Scrabble US: M 3, U 1, L 1, T 1, I 1, V 4, A 1, L 1, E 1, N 1, T 1.

Is it a valid word?

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

used of the association of three or more homologous chromosomes during the first division of meiosis
having more than one valence, or having a valence of 3 or higher
having many values, meanings, or appeals

Also: multi-valued.