Yes, RELATIVE is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, L 1, A 1, T 1, I 1, V 4, E 1.

Is it a valid word?

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

a person related by blood or marriage
an animal or plant that bears a relationship to another (as related by common descent or by membership in the same genus)

estimated by comparison; not absolute or complete
properly related in size or degree or other measurable characteristics; usually followed by `to'

Not playable in Scrabble US: CONGENATOR.