Hello
"What does it mean? Is it just that it never was tested?"
Generally this means that the vendor (Dell in this case) stopped supporting the product as end-of-life and thus stopped creating new custom iso bundles for these servers with new releases of ESXi (6.0 in this case).
Alternatively, some hardware does not go on the Hardware Compatibility List for some ESXi versions due to issues with how they performed (e.g. incompatible).
http://www.vmware.com/resources/compatibility/detail.php?deviceCategory=server&productid=13819&vcl=t...
"What problems will I encounter if I ignore the list and install 6.0?"
There is no simple answer to this - it might run normally (or run okay until it does not) or it might have serious issues which there is no solution to.
If you do choose to ignore the HCL and install 6.0 then bear in mind that any vendor or VMware support will be well within their rights to not entertain the idea of assisting with any issues that arise as a result of this (as there may be no solution and doing so would be a waste of resources).
Is there some urgent need to use 6.0? If there is then you should consider upgrading to hardware that was intended to function with modern releases of ESXi.
Bob
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