They do. Sometimes things will work perfectly fine on the test server and then go all to hell once it's pushed to the live server.
You'd have to be a special kind of stupid to think they just blindly shove things directly onto a live server environment without even the barest amount of QC to make sure everything is fine. And please, spare me the "hurr durr nexon am retards" memes. Nobody who runs or maintains servers of any sort would be stupid enough to do that, and if they did they would soon find themselves out of a job.