In a "Failure to Feed" jam (FTF), the old casing is extracted and ejected fine, but the new round nose dives into the feed ramp on its way into the chamber, keeping the round from chambering, and keeping the slide from closing. Typically caused by a bad magazine or JHP rounds with too much 'hollow' to allow the bullet to run up the feed ramp. If he's tried several mags and is using FMJ, I don't see how this could be it.
In a "Failure to Extract", the old casing never leaves the chamber, and if the new round is stripped by the slide at all, its nose will slam into the primer area of the spent case which is still in the chamber, and the slide will obviously not close. I'm not sure what can cause this, or how the slide is cycled on a recoil operated gun without the old casing leaving the chamber, but its happened first hand to me while shooting a friend's kel-tec P32. Might want to look at the extractor.
A "Failure to Eject" and a "Stovepipe" are basically the same thing. It happens when the spent casing is extracted, but does not clear the action in time, and is "caught" between the barrel and the slide as the slide is closing on the next round. This is typically caused by a bad ejector, or recoil spring tension could be out of spec.
A brand new Sig shouldn't be experiencing any of these problems after 1200 rds. I still say send it back.