Yes, LUMPERS is a Scrabble word!

Letter values in Scrabble US: L 1, U 1, M 3, P 3, E 1, R 1, S 1.

Is it a valid word?

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

a laborer who loads and unloads vessels in a port
a taxonomist who classifies organisms into large groups on the basis of major characteristics

Also: dock worker, dock-walloper.