Yes, CAUL is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, U 1, L 1.

Is it a valid word?

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

part of the peritoneum attached to the stomach and to the colon and covering the intestines
the inner membrane of embryos in higher vertebrates (especially when covering the head at birth)

Also: greater omentum, gastrocolic omentum, embryonic membrane.