Yes, STIPPLING is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, I 1, P 3, P 3, L 1, I 1, N 1, G 2.

Is it a valid word?

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

engrave by means of dots and flicks
make by small short touches that together produce an even or softly graded shadow, as in paint or ink
apply (paint) in small dots or strokes
produce a mottled effect