I came across an issue earlier where I wanted to nest ESXi on an ESXi host - something that is well documented (by William Lam in particular). The issue I had was that I hadn't yet deployed a vCenter server and didn't want to do so outside of my nested ESXi environment. This is so I could contain the vCenter on the cluster of nested ESXi hosts rather than outside on the top-level host.
The issue is that to get nested ESXi working, from within the web client (part of vCenter) you have to expose the NX/XD flag to guest and check the 'Expose hardware assisted virtualisation to the Guest OS':
(Image courtesy of http://wojcieh.net/)
The reason behind this is that if the virtualisation features of the CPU are not exposed to the guest, you will get the following error:
To do this without a vCenter, you have to modify the nested host's (or the 'VMs' depending on your perspective) VMX file to include this feature. Comparing to a VM I changed with the vCenter, I found there were an additional two lines:
Found using https://www.diffchecker.com which is an online comparison tool.
To add these lines into the VMX file, I started by SSHing to the host (the actual host - not the virtual host / nested host):
CD to /vmfs/volumes/<whereveryourvmresides> and VI the .vmx file:
Add the additional two lines as shown above - and you will be able to deploy your VCSA or any other VM onto the nested ESXi host without using the web client.