I'm running a virual environment of this sort.
There's a UCS box that has several VMs. I've setup 3 Virtual ESXi VMs and vCenter Server appliance. Using the appliance, I installed 3 WinXP VMs on the ESXis. (One on each ESXi).
The IP that I've allocated to the WinXP VM are in the same broadcast domain as that of the ESXi hosts (10.0.0.x/24).
But, they don't ping each other.
EDIT: FW settings have been sorted. They still don't communicate. What's interesting is that the ESXis hosts, themselves can communicate with each other, but the underlying VMs that are in the same broadcat domain can't communicate.