Hypervisors have their own security issues. They're just programs. That's why there've been all the patching over the years for Xen and for KVM.
Last year, an independent researcher did find an issue related to Dtrace that Joyent patched. However, the security and engineering that backs Zones is way more than with other kernels.
https://www.joyent.com/blog/dtrace-conf-16-wrap-up
DTrace exploitation: http://slides.com/benmurphy/deck#/
http://benmmurphy.github.io/blog/2017/01/06/arbitrary-kernel...
Apropos "KVM-inspired hypervisor": the zones still function in exactly the same way as they did when I first used them in 2006; in fact when running lx and KVM Joyent is exploiting an obscure capability called a brand (branded zones), but that capability has always been there, since day one back in 2006.
Finally, there has only been one known case of managing to break out of a zone and this was through a kernel driver exposed to it, exactly the kind of scenario you'd have on VMware. In the decade since, there have been no known cases, so not only is your argumentation cookamamie, it's in the realm of pure hypothesis.
In fact, if you look into Joyent, you'll see they don't use regular zones for multi-tenancy, but rather a KVM-inspired hypervisor implementation of zones.