vCenter Server 5.1.0 Build 1123961
ESXi 5.1.0 Build 1483097
VM Hardware version 9
vmxnet3 driver
We are seeing an issue where when we update VMware Tools the A-record on our DNS server is removed for that VM. The only way to resolve the issue is to "ipconfig /registerdns" which I feel is find for a band-aid, but not a good solution.
It seems as though others have had this same issue in the past without any real VMware resolution.