is there any ConfigMgr reason I can't just pull the hard drives and put them in a newer server? Is ConfigMgr in anyway 'aware' of or tied to the specific hardware it's on?
At the ConfigMgr level, there is no problem that prevents you from pulling the hard drives and putting them on a newer server.
Factors that may affect your success in pulling the hard drives and putting them on a newer server may depend on whether the hard disk drive is compatible with the hardware of the replaced server.
You may try to this, if you encounter compatibility issue, then you may use ConfigMgr Site Backup and Restore:
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