Yes, REINDEER is a Scrabble word!

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

Is it a valid word?

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

Arctic deer with large antlers in both sexes; called `reindeer' in Eurasia and `caribou' in North America

Also: greenland caribou, rangifer tarandus.