Totally, absolutely, positively, and undeniably sure. Dell Support was wrong and they should have known better. The memory controller is on the processor not on the system board, so without a processor the memory slots can't be used. The only way to have 64GB of RAM with a single processor is 4x16GB. There is lots of relevant documentation. Running ESXi, I'm not sure why you wouldn't have two processors any way ...
Hi there, I have  a R510 poweredge server with 1 processor (Intel(R) Xeon(R) CPU E5630  @ 2.53GHz) It used to have 12Gb (3x4Gb) of ram, but i've decided to do an upgrade. I have purchased these modules:  8 x 8GB PC3L-10600R DDR3 1333 ECC Reg, that is a total amount of 64Gb Unfortunately, the system recognizes only the 32Gb. I have also tried to use just the 4 modules on the slots next to the empty cpu slot, but the system didn't boot cause it couldn't see any ram installed. Can you please help?  Thank you in advance. 
Poweredge R510 only recognizes 32Gb RAM (of total 64Gb)