Yes, RETAINERS is a Scrabble word!

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

Is it a valid word?

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

a fee charged in advance to retain the services of someone
a person working in the service of another (especially in the household)
a dental appliance that holds teeth (or a prosthesis) in position after orthodontic treatment