Yes, MARROWS is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, R 1, R 1, O 1, W 4, S 1.

Is it a valid word?

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

the fatty network of connective tissue that fills the cavities of bones
any of various squash plants grown for their elongated fruit with smooth dark green skin and whitish flesh
very tender and very nutritious tissue from marrowbones
large elongated squash with creamy to deep green skins
the choicest or most essential or most vital part of some idea or experience

Also: bone marrow, marrow squash, vegetable marrow, heart and soul, nitty-gritty.