I would look at the Security Properties of the vSwitch and Port Group
You are talking about nested ESXi?? If yes, the network Switch here the Nested ESXi is connected needs to have promiscuous mode enabled.
If you want your VMs to communicate with your physical network, make sure your NIC is configured as bridge in Workstation.
Thanks for the replies.
Turns out our network guy hadn't actually enabled DHCP on the subnet range /facepalm