My initial thoughts: It's possible that since the virtual machine is running on a virtualized CPU, Apple's Hypervisor Framework might not be able to provide access to the low level hardware information needed to get the temperature information. It may not be relevant either, since a virtualized cpu runs on a user-mode thread, and macOS controls both the frequency of the core being used and the type of core. The guest has no control over either of those, and therefore has no way to modify its behavior to reduce its CPU thermal impact.
Some additional research says that thermal monitoring works very differently between Apple Silicon and Intel chips. SInce the guest isn't controlling temperature (or CPU frequency) for a virtual CPU, a better idea may be to monitor temperature from the host side. A utility that seems to be recommended by many in the research I've done is Hot (https://github.com/macmade/Hot).