Yes, REDSHIFT is a Scrabble word!

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

Is it a valid word?

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

(astronomy) a shift in the spectra of very distant galaxies toward longer wavelengths (toward the red end of the spectrum); generally interpreted as evidence that the universe is expanding

Also: red shift.