There are no dedicated Diamond agents, with the expection of the 360 line. There hasn't been for years.
Agents in MSP, CVG, SLC, and Chisholm take all of the Gold, Platinum, and Diamond calls. I think Dallas too, but I'm not sure.
When call volume is significantly elevated, TPA and ATL will sometimes get excess Gold, Platinum, and Diamond calls, but that's pretty rare from what I understand.