lol Running Linux/390 or z/Linux under Hercules just slows the thing down, without offering any mainframe benefits.
Not even educational benefits, as you can not license z/VM, VM/ESA, z/OS or OS/390 to Hercules to run a Linux in the same environment as it would on a real iron.
It's actually very useful for developing, testing and debugging programs that need to be run on a mainframe without having to actually try it out directly on your production environment.
The main point of z/VM is that you can run multiple instances of different operating systems on the same physical hardware. (It's sort of amazing that IBM started developing this virtualization software in the mid-1960s.)
And you can most certainly tell it's there, since there's an API to call z/VM services (which wouldn't exist on the bare hardware) from a virtual machine:
I really wish IBM would open up some sort of emulation environment for educational use. Their customers desperately need new z/OS developers but it's hard to break into that space and learn it.
Not even educational benefits, as you can not license z/VM, VM/ESA, z/OS or OS/390 to Hercules to run a Linux in the same environment as it would on a real iron.