Looking at the Intel ARK site, https://ark.intel.com/compare/96486,96485
Both x5-e3xxx CPUs have
VT-x - required regardless of ESXi version
EPT - gives faster VM memory performance, required for VMX Unrestricted Guest feature, required for 64-bit nested VMs to run
VT-d - required for device passthrough, although this is not the only requirement for device passthrough to work
Execute Disable bit - required if guest VM OS requires it (e.g. Windows Server 2012)
AES instruction set - not required per se but gives faster encryption/decryption for both host and guest VMs
So there isn't real obvious deterrent for these CPUs to run ESXi unless the motherboard design and/or EFI/BIOS disables any of the features above.
The downside is that both CPUs are limited to maximum of 8GB RAM. Both also have low TDP and targeted for embedded devices and therefore the CPU might be in a fanless design and throttled down heavily during heavy loads.
There is no harm in trying to install ESXi for learning purposes. But any problem faced during install and/or running of ESXi, support can be difficult to obtain (official or unofficial such as through the community) as these CPUs (and their associated motherboards) are not commonly used in servers, desktops, and laptops.
