Q: Can I use a single
A: While there are separate images for Windows Server 2012 Standard and Windows Server 2012 Datacenter on the installation media, in reality Standard and Datacenter are identical OSs, bit for bit. They have the same scalability and the same features.
The only difference between Standard and Datacenter is the licensing for number of included virtual machines (VMs): 2 for Standard, unlimited for Datacenter. However, there's no hard-coded limit that stops a Standard Hyper-V deployment from running more than two VMs.
Microsoft only provides different images to help organizations track where they need Standard licenses and where they need Datacenter. This means while you might need to purchase Datacenter licenses for your Hyper-V hosts it would be no issue to install Windows Server 2012 Standard on the actual host.
Just make sure in your organization you have some tracking of where the Datacenter licenses are actually assigned. This means the organization could just use a single Windows Server 2012 Standard image for the Hyper-V hosts, VMs, and the physical servers.
Another option that builds on the previous single image is to deploy the Windows Server 2012 Standard image to Hyper-V hosts (which is typically the only place Datacenter will be used since Standard is functionally identical to Datacenter) and then use DISM to convert the Standard installation to Datacenter, which I explain how to do in the FAQ "Can I switch a Windows Server 2012 Standard Server to a Windows Server 2012 Datacenter Server?" This will make it easier to track where Datacenter licenses are actually being used.