Yes, DISTEMPER is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, S 1, T 1, E 1, M 3, P 3, E 1, R 1.

Is it a valid word?

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

any of various infectious viral diseases of animals
an angry and disagreeable mood
paint made by mixing the pigments with water and a binder
a painting created with paint that is made by mixing the pigments with water and a binder
a method of painting in which the pigments are mixed with water and a binder; used for painting posters or murals or stage scenery

Also: ill humor, ill humour.