Question: can Hyper-V and VirtualBox coexist on the same machine?

Question: can Hyper-V and VirtualBox coexist on the same machine i.e. be installed at same time? NO.

 But it seems there is a registry hack in Windows that will let you do it anyways.

This is basically due to the fact that Hyper-V is a Type 1 hypervisor and VirtualBox is a Type 2 hypervisor.