I've inherited an Apple Mac Xserve Cluster:-
and as these are Xserve 3,1 are on the HCL for ESXi 5.5. Therefore I can legally accept the Apple EULA, and install Apple macOS Virtual Machines on them, because they have an Apple badge (Apple hardware).
If you do not have an Apple badge on your hardware, you are in breach of the Apple EULA. (Please do not ask me, because this cannot be discussed on Experts Exchange)