It won't stop a private individual, either, not even one with a budget of approximately $0. Cold boot and similar attacks, even just yanking the memory or forcing a CMOS reset, are trivial. Please tell me you don't do this for a living.

We are talking about live servers. Monitoring should detect server going down, raising suspicion of a physical attack.

The evil maid attack would be useful against the system admin's workstation. Securing NOCs is beyond the scope of this discussion, but it is not difficult.