Yes, WHIST is a Scrabble word!

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

Is it a valid word?

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

a card game for four players who form two partnerships; a pack of 52 cards is dealt and each side scores one point for each trick it takes in excess of six

Also: long whist, short whist.