Yes, WHIN is a Scrabble word!

Letter values in Scrabble US: W 4, H 4, I 1, N 1.

Is it a valid word?

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

very spiny and dense evergreen shrub with fragrant golden-yellow flowers; common throughout western Europe
small Eurasian shrub having clusters of yellow flowers that yield a dye; common as a weed in Britain and the United States; sometimes grown as an ornamental
any of various hard colored rocks (especially rocks consisting of chert or basalt)

Also: irish gorse, ulex europaeus, dyer's greenweed, dyer's-broom, genista tinctoria.

Not playable in Scrabble US: GREENWEED.