Untrue! He had *nothing* to do with Opteron. He has been around succesful designs and is certainly knowledgeable on them but he has not been the chief architect for any of the shipping Apple or AMD parts.
Keller was one of the engineers behind Opteron, the generation that really made an innovative leap over Intel by integrating the memory controller and a coherent bus (HyperTransport) on a server chip.
AMD needs some of that leap ahead product innovation today. It now has all the pieces in place with leading graphics cores, multiple x86 cores, an ARM partnership--and now a returning veteran microprocessor designer.