I don't know with which licensing you operate assuming it is Server 2012 licensing model which is completely different from previous on 2008 Servers...
First Datacenter license is only worth if your environment has plenty of VMs and gradually increase in numbers ...
For low density virtual environments for example 50 VMs/on 8+ blades or an absurd scenario of 10VMs per 8 blades your choice is definitely Standard licensing.
One Standard edition license entitles up to two VOSEs on up to two processors (2 socket server) = 8x Standard license enables you to run up to 16 VOSEs on 8 blades...
For detailed and precise licensing info see this document:
So lets say you only had 10 VM's and 8 Physically servers, yes this does seem unrealistic, but just for the sake of argument, If I had one HA cluster with 8 physical servers
then i would have to buy 5 Microsoft licenses for each physical server. So 40 licenses total. Or buy 8 Datacenter licenses. In this case buying individual licenses would probably be cheaper then the datacenter licenses.
Why 5 MS licenses for 1 physical server ??? With Server 2012 licensing model you only need 1MS Standard license per Blade for example above.
But if I split it up into two HA clusters, so 5 VM in each HA cluster, and say 4 physical servers in each Cluster (yes that's allot of physically servers for so little VM's, just an example),
so then I would need allot less Microsoft individual licenses as long as the VM's never get moved over to the other physical hosts.
Is that allowed, I just don't want to break any Microsoft Licensing. Im assuming its just on me to make sure the VM's never get migrated to the other hosts.
Yes you can use DRS affinity rules to restrain VMs only to licensed hosts but regarding this I would ask some MS licensing specialist or license supplier.
For more on that read "Q: What are my licensing options for the recovery server as part of disaster recovery planning?" section of document above.