I am looking for and have not found where the user interface of Windows Server 2012's AD and Server Management tools, I can see the replication status of domain (Active Directory) data replication, similar to the stuff that you could query using dfsrdiag
from the command line.
Is there something built in? I have found an installable tool ADREPLSTATUS
that may offer some of this information, but I am wondering if there is any built in UI for this.
I have searched the Active Directory Administrative Center and the Server Manager to no effect.
No. The old Replmon went out of style a long time ago. See the AskDS post "Getting over Replmon":
http://blogs.technet.com/b/askds/archive/2009/07/01/getting-over-replmon.aspx
The idea is that repadmin, a command-line tool, can do everything and more that the GUI Replmon could do, only faster and more efficiently.
Then, if you still just really can't stand not having a GUI, then you can install AD Replication Status Tool, which you have already found.
http://www.microsoft.com/en-us/download/details.aspx?id=30005
Here's the AskDS post about that tool when it released just about a year ago:
http://blogs.technet.com/b/askds/archive/2012/08/23/ad-replication-status-tool-is-live.aspx
Edit: Just to clarify, the standard suite of Remote Server Administration Tools such ADUC, Sites and Services, ADSI Edit, etc., are of course still included with Server 2012. You'll get them automatically on a DC, or on any member server if you install the RSAT optional feature. But for monitoring replication status, it's the repadmin command line tool, or the downloadable AD Replication Status tool.