Are there stats for a cherub or would they be the same as a servo skull?

As far as I know, stats for Cherubim can be found in "The Inquisitor's Handbook" (standard Cherubim) as well as in "Blood of Martyrs" (Self-Flagellant version).

Those are the only official sources for them, yes. There's also http://darkheresy.wikia.com/wiki/Servants