I found two things out related to this issue:

1.  The Supermicro systems we are running (i.e. SYS-5018A-FTN4) are running with a HCL supported processor (Atom C2758), but the motherboard that comes with this system apparently is now only supported to vSphere 6 (https://www.vmware.com/resources/compatibility/search.php?deviceCategory=server&productid=43366&devi...)

2.  Supermicro doesn't seem to see this as an issue and won't be releasing a firmware update to fix it.

Is there a way to disable the microcode version check at boot time for these systems?