Xen, OpenVZ, Virtuozzo… you can try any you want, but SlickStack community will not “help” you if you are having problems because of the non-KVM server
We don’t test non-KVM servers… we believe KVM is the future of cloud servers, at least for next several years.
If you find a bug or config in SlickStack that is causing problems with these other virtualizations you can open a GitHub issue and we are happy to make small changes if it means better support for other environments, but we just don’t prioritize testing them.