As I understand it, Windows Server 2012 R2 is fully supported as a VM on ESXi 5.5 hosts but when I go to create a new VM the latest OS I see in the list is 2012. Am I missing something?
2012 R2 is not listed in New vm entry yet. but it will support on 2012 R2 as well. So you can continue creating the vm with 2012 ..
2012R2 is fully supported in vSphere 5.5. As you can see in the post the announcment came on 17-10-2013 which is after the vSphere 5.5 release on 2013-09-22. That is the reason we dont see 2012R2 in the GOS list in vSphere client.
However since its supported you can safely go ahead with the option 'Windows 2012'. It will work.