I should mention that we also have one W2012 server that DOES work properly. It is the one that actually hosts the SQL database. The GP client is installed on that server, and the XML renders as expected. All of these W2012 servers are running in VMware ESXi 5.1. Yesterday, I built a brand new VM from scratch, and then installed GP on it, and it still didn't work properly. I even tried installing SQL 2012 on it, and no dice.
This is extremely frustrating. We requested a call-back from MS on Tuesday, but we have yet to hear from them. I'm going to be in a lot of hot water if I can't get this working very soon...