Yes, BANNERETS is a Scrabble word!

Letter values in Scrabble US: B 3, A 1, N 1, N 1, E 1, R 1, E 1, T 1, S 1.

Is it a valid word?

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

a knight honored for valor; entitled to display a square banner and to hold higher command

Also: knight banneret, knight of the square flag.