Yes, UNDERCOATS is a Scrabble word!

Letter values in Scrabble US: U 1, N 1, D 2, E 1, R 1, C 3, O 1, A 1, T 1, S 1.

Is it a valid word?

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

seal consisting of a coating of a tar or rubberlike material on the underside of a motor vehicle to retard corrosion
the first or preliminary coat of paint or size applied to a surface
thick soft fur lying beneath the longer and coarser guard hair

Also: flat coat, primer coat, priming coat.

Not playable in Scrabble US: UNDERSEAL.