Yes, DATELINE is a Scrabble word!

Letter values in Scrabble US: D 2, A 1, T 1, E 1, L 1, I 1, N 1, E 1.

Is it a valid word?

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

an imaginary line on the surface of the earth following (approximately) the 180th meridian
a line at the beginning of a news article giving the date and place of origin of the news dispatch

Also: date line, international date line, date-mark.

Not playable in Scrabble US: DATEMARK.