O que você está perdendo, até onde eu sei, é que o NPS não é uma função suportada no Server 2012 Core . (Mesmo que RRAS seja.)
When Windows Server 2012 is in Server Core mode, the following server roles are supported:
Active Directory Certificate Services
Active Directory Domain Services
DHCP Server
DNS Server
File Services (including File Server Resource Manager)
Active Directory Lightweight Directory Services (AD LDS)
Hyper-V
Print and Document Services
Streaming Media Services
Web Server (including a subset of ASP.NET)
Windows Server Update Server
Active Directory Rights Management Server
Routing and Remote Access Server, including the following sub-roles:
Remote Desktop Services Connection Broker
Licensing
Virtualization