Yes, PAINTER is a Scrabble word!

Letter values in Scrabble US: P 3, A 1, I 1, N 1, T 1, E 1, R 1.

Is it a valid word?

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

an artist who paints
a worker who is employed to cover objects with paint
a line that is attached to the bow of a boat and used for tying up (as when docking or towing)
large American feline resembling a lion

Also: mountain lion, felis concolor.