Yes, LIMBS is a Scrabble word!

Letter values in Scrabble US: L 1, I 1, M 3, B 3, S 1.

Is it a valid word?

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

one of the jointed appendages of an animal used for locomotion or grasping: arm; leg; wing; flipper
any of the main branches arising from the trunk or a bough of a tree
(astronomy) the circumferential edge of the apparent disc of the sun or the moon or a planet
either of the two halves of a bow from handle to tip
the graduated arc that is attached to an instrument for measuring angles
any projection that is thought to resemble a human arm

Also: tree branch.