Yes, VANGUARD is a Scrabble word!

Letter values in Scrabble US: V 4, A 1, N 1, G 2, U 1, A 1, R 1, D 2.

Is it a valid word?

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

the leading units moving at the head of an army
any creative group active in the innovation and application of new concepts and techniques in a given field (especially in the arts)
the position of greatest importance or advancement; the leading position in any movement or field

Also: avant-garde, new wave, cutting edge.