Yes, RATTING is a Scrabble word!

Letter values in Scrabble US: R 1, A 1, T 1, T 1, I 1, N 1, G 2.

Is it a valid word?

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

to furnish incriminating evidence to an officer of the law (usually in return for favors)

desert one's party or group of friends, for example, for one's personal advantage
employ scabs or strike breakers in
take the place of work of someone on strike
give (hair) the appearance of being fuller by using a rat
catch rats, especially with dogs
give away information about somebody

Also: tell on, give away.