As per the Release Notes for Archive Manager 4.4.2 and in all versions since Archive Manager 4.3.1, Windows Server 2008 R2 is supported:
Prerequisites for all servers running Archive Manager Services
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Operating system must be one of:
Microsoft Windows 2008 Server SP2, 64-bit version.
Microsoft Windows 2008 R2 Server, 64-bit version.
Microsoft Windows 2003 Server SP1 or SP2, 32-bit version.
Microsoft Windows 2003 Server R2 SP2, 32-bit version.
