Squawk[0] ran pretty much directly on the hardware, Sun had a JVM-on-Xen project, OSv provides a lightweight pseudo-OS (not unlike rump kernels it looks) which support JVMs. Possibly one step down, Oracle has a JRockit VE edition which runs directly on the Oracle Hypervisor, but despite being Xen-based it's unclear whether that can run on raw hardware.

[0] https://en.wikipedia.org/wiki/Squawk_virtual_machine