Look, from a legal perspective this is a matter of civil procedure. For Apple to enforce this agreement it has to first discover your usage and then prove its damages in a court. The damages would likely be the cost of Mac hardware of equivalent power to the VMs plus legal fees.

What this means is that no one should spin up a server farm of OS X VMs and then blog about it. For everyone else, Apple is not going to discover you and if they do they are not going to pursue damages against you for the cost of a Mac Mini. Apple is just not out there doing that type of lawsuit