For domestic flights in the US, when your boarding pass is scanned at the gate, does the gate agent make sure that pass was also scanned at security?
Except for one experimental program, the two aren't connected. CAT/BPSS is still being 'tested'. (Note, I'd totally forgotten about this so after following up, it appears that even CAT/BPSS is not real-time, it's merely a better document verification system.)
The scanners TSA currently uses validate some facets of the boarding pass, but are otherwise isolated.