Yes, EXISTENT is a Scrabble word!

Letter values in Scrabble US: E 1, X 8, I 1, S 1, T 1, E 1, N 1, T 1.

Is it a valid word?

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

having existence or being or actuality
being or occurring in fact or actuality; having verified existence; not illusory; not ghosts"
presently existing in fact and not merely potential or possible