Yes, SCALLION is a Scrabble word!

Letter values in Scrabble US: S 1, C 3, A 1, L 1, L 1, I 1, O 1, N 1.

Is it a valid word?

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

plant having a large slender white bulb and flat overlapping dark green leaves; used in cooking; believed derived from the wild Allium ampeloprasum
a young onion before the bulb has enlarged; eaten in salads

Also: allium porrum, green onion, spring onion.