Licensing around running VMWare ESX on a mac mini hosting multiple OS X guests The OS X Mavericks EULA grants the rights


  B. 
  Mac App Store License
  
  ...
  
  (iii) to install, use and run up to two (2) additional copies or instances of the Apple Software within virtual operating system environments on each Mac Computer you own or control that is already running the Apple Software, for purposes of: (a) software development; (b) testing during software development; (c) using OS X Server; or (d) personal, non-commercial use.


By my reading, this implies that I can't use VMWare ESX as the base-level OS hosting OS X guests, as then it wouldn't be "already running the Apple Software". However, VMWare definitely support running OS X as a guest under VMWare ESX. Presumably VMWare wouldn't support something that violates the OS X EULA, or they would have continued the support for OS X guests running under VMware workstation on windows that they had for a short time.

How does this add up?

Also, If we assume that it is OK, what happens if I want to run 3 or 4 guest copies of OS X on my mac mini? The EULA implies that it's not, however the EULA also contains this clause


  C.
  Volume or Maintenance License.
  If you obtained the Apple Software under a volume or maintenance license program with Apple, the terms of your volume or maintenance license will determine the number of copies of the Apple Software you are permitted to download, install, use and run on Apple-branded computers you own or control. Except as agreed to in writing by Apple, all other terms and conditions of this License shall apply to your use of the Apple Software obtained under a volume or maintenance license


This seems like it would provide a solution to both of the above, but I can't figure out if it's possible to purchase a "Volume or Maintenance License" for OS X, as nothing I've been able to find on their website has any information related to it.

Thanks
The OS X EULA does allow for OS X to be virtualized on Apple hardware as both host and guest.  This is why (as you note) VMware Workstation does not support OS X virtualization, but Fusion, ESXi, and vSphere do.  All versions of VMware's apps check to ensure that you are running on Apple hardware and you are running a supported OS (as not all versions of OS X allow virtualization).  

Apple doesn't make it easy to purchase a Volume License.  You either need to buy it directly from Apple (it's not on their website, you have to call them) or through a third-party reseller.  

You are completely correct that the EULAs are unclear about the question of running 3+ OS X VMs on a single OS X host.  This is a legal question, and not a technical one.  For that matter, so is the limitation about which versions of OS X can be virtualized (ex: 10.6 virtualization requires the Server edition, and all VMware applications block you from virtualizing the Standard edition).  If the EULA were clear that you could not virtualize 3+ OS X VMs, or if Apple had said anything to VMware about it, VMware could limit you to 2 OS X guests per OS X host.

If virtualizing OS X is your goal, you should talk with someone who is in Apple Enterprise Sales about what you want to do.  EULA questions really can't be answered in any meaningful way by anyone else.