Yes, RETEM is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, T 1, E 1, M 3.

Is it a valid word?

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

desert shrub of Syria and Arabia having small white flowers; constitutes the juniper of the Old Testament; sometimes placed in genus Genista

Also: juniper bush, retama raetam, genista raetam.

Not playable in Scrabble US: RAETAM.