No, unavailability of virtualisation happens in Windows 8 if you have Hyper-V enabled even if you are not running a Virtual Machine. This is because Hyper-V, unlike VMware or VirtualBox which are type 2 hypervisors, is a type 1 or "bare metal" hypervisor. If enabled Hyper-V loads before the host OS and virtualises both that and any guest OSs so making virtualisation unavailable to any other virtuualiser.
VMware and VirtualBox only start virtualisation when they start a VM so you can have both VMware and VirtualBox installed on a machine and run one or the other but not both at the same time. Neither can run if Hyper-V is enabled on a Windows 8 system.