Yes, RHACHISES is a Scrabble word!

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

Is it a valid word?

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

axis of a compound leaf or compound inflorescence
the series of vertebrae forming the axis of the skeleton and protecting the spinal cord

Also: spinal column, vertebral column.