>Pretty much every cloud outside the big three (AWS, GCE, Azure) runs on QEMU.
QEMU typically uses KVM for the hypervisor, so the vulnerabilities will be KVM anyway. The big three all use KVM now. Oxide decided to go with bhyve instead of KVM.
No, QEMU is a huge C program which can have its own vulnerabilities.
Usually QEMU runs heavily confined, but remote code execution in QEMU (remote = "from the guest") can be a first step towards exploiting a more serious local escalation via a kernel vulnerability. This second vulnerability can be in KVM or in any other part of the kernel.
QEMU typically uses KVM for the hypervisor, so the vulnerabilities will be KVM anyway. The big three all use KVM now. Oxide decided to go with bhyve instead of KVM.