Your assessment sounds about right. I'm not leaning towards the "bricked" configuration just yet, mainly because the WP configuration was simply enabling the caching. Nothing else. The configuration change we added later to override the domain name was after we discovered the cache had been holding all the user passwords (and not the database).
Anyway, does anyone on here have any suggestions at where in the code might be a good starting point? The object-cache.php file? or are there other spots? I am also willing to see this as a configuration issue, as the person who set this up a year ago might have done something funky. But I also don't know where I should start looking for that. Nginx conf files? WP?