Yes, KUMQUATS is a Scrabble word!

Letter values in Scrabble US: K 5, U 1, M 3, Q 10, U 1, A 1, T 1, S 1.

Is it a valid word?

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

any of several trees or shrubs of the genus Fortunella bearing small orange-colored edible fruits with thick sweet-flavored skin and sour pulp
small oval citrus fruit with thin sweet rind and very acid pulp

Also: kumquat tree.