In-place upgrade of Windows Server 2008 (not R2) to 2012
Yes, you can upgrade to the non-R2 edition of Windows Server 2012.
If you are running:
Windows Server 2008 Standard with SP2 or Windows Server 2008 Enterprise with SP2
You can upgrade to these editions:
Windows Server 2012 Standard, Windows Server 2012 Datacenter
Then if you want to upgrade to 2012 R2 from regular 2012 you can do that whenever.