Hi @Andrea Dillon
Of course you can. You don't find nothing specific to datacenter r2 because both versions (standard and Datacenter) are eligible for in-place upgrade. I have alreday performed a upgrade in place without any issue in my test envirement for more information please read the following article:
Overview of Windows Server upgrades
For your information , microsoft recommend to avoid a upgrade in place and migrate the service to new server installed from scratch.
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