OpenVZ is a container style virtualisation, whereas KVM is full virtualisation.
Technically they are very different, and KVM requires VT-x CPU features on Intel CPUs, or AMD-V features on AMD CPUs.

Your VM is complaining, because it isn't seeing these features, as Virtualbox isn't presenting these CPU features to your Virtualizor VM.

If you have an AMD CPU, you may be in luck, as it looks like you can enable nested virtualization (https://forums.virtualbox.org/viewtopic.php?f=1&t=90831) which would allow you to run KVM VM's from within your Virtualbox VM.