Solved Is Uber Diablo a server-side event now?

This is possible and it's actually part of the original game. Basically, this is how the DClone spawns in Diablo II while the guaranteed SoJ sale is the custom feature of this server therefore, there are two situations in which the Diablo Clone can spawn:
1. By selling one SoJ to the vendor in a Hell difficulty game (this will spawn DClone in your own game, guaranteed)
2. Randomly, after a number of total SoJ has been sold in one particular server
There's even a dedicated guide thread where you can read about how Diablo Clone works http://forum.europebattle.net/threads/diablo-clone-hunting-how-to-get-annihilus.539750/