Yes, INDIFFERENT is a Scrabble word!

Letter values in Scrabble US: I 1, N 1, D 2, I 1, F 4, F 4, E 1, R 1, E 1, N 1, T 1.

Is it a valid word?

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

marked by a lack of interest; it is simply indifferent"
showing no care or concern in attitude or action
(usually followed by `to') unwilling or refusing to pay heed
(often followed by `to') lacking importance; not mattering one way or the other
fairly poor to not very good
having only a limited ability to react chemically; chemically inactive
marked by no especial liking or dislike or preference for one thing over another
characterized by a lack of partiality
being neither good nor bad
neither too great nor too little

Also: so-so.