User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-170.235.245.51-20130606171516/@comment-3146930-20130606205832

The Greek side of the gods were fighting Typhon at the time. It is unknown if they know exactly what Camp Jupiter did, as Hermes only tells Percy that Mount Othrys crumbled after Kronos' defeat. Camp Jupiter also doesn't really mention any gods helping (I think in The Son of Neptune, that any kind of godly visit is rare), so Camp Jupiter might not have been watching the gods fighting Typhon. Even if their Roman sides somehow helped the Camp Jupiter army, neither personality would tell their respective camps about their Greek or Roman forms. They want to keep the camps apart, so they wouldn't openly admit to there being another camp to either side.