Question #1: I've been screened 4 out of the last 5 arrivals NRT-IAD on UA/NH that lands late at night. There are multiple flights arriving at the nearly the same time in same terminal so not sure if that's a factor.
Be prepared for bags to be checked. If I were you, I would bring your chew on your person, not bags. Nobody's going to jail for this. They will likely just confiscate if discovered, with a warning.