Yes, NICHES is a Scrabble word!

Letter values in Scrabble US: N 1, I 1, C 3, H 4, E 1, S 1.

Is it a valid word?

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

a position particularly well suited to the person who occupies it
a small concavity
an enclosure that is set back or indented
(ecology) the status of an organism within its environment and community (affecting its survival as a species)

Also: ecological niche.