Usually for upgrades of big production stacks I would recommend going to 3.2 first as an intermediary and do extensive testing before trying again to 3.3, and always use the CLI upgrader, don't use the web one if you have CLI access.
To isolate plugins, why not clone the environment, uninstall all plugins and run the upgrade? That would rule it out.
That said, I wouldn't think so, since it's failing on upgrade_core(). Hopefully a developer sees this and can give better insight.