Yes, SIMILAR is a Scrabble word!

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

Is it a valid word?

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

marked by correspondence or resemblance
having the same or similar characteristics
resembling or similar; having the same or some of the same characteristics; often used in combination
(of words) expressing closely related meanings
capable of replacing or changing places with something else; permitting mutual substitution without loss of function or suitability