Yes, METHODISTS is a Scrabble word!

Letter values in Scrabble US: M 3, E 1, T 1, H 4, O 1, D 2, I 1, S 1, T 1, S 1.

Is it a valid word?

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

a Protestant denomination founded on the principles of John Wesley and Charles Wesley
a follower of Wesleyanism as practiced by the Methodist Church

Also: methodist church.