Any computer, even an Android phone, can be used as a server. The issue is MTBF and maintenance in numbers. ECC might be not that important if your workload is not critical and you have a correct reboot policy.

Lack of BMC like IPMI is much worse, meaning you will need to hop on a trip or ask someone at the installation site to check your HW.

So what makes a server server is probably a mix of remote maintenance capabilities and redundancies to minimize said maintenance.