As far as I understand HT, whether in the context of virtualisation or plain bare-metal OS, the use of the hyperthread pair is in generally in the hands of the CPU. Since the hyperthread pair share the same L1/L2 cache (as well as execution engine), being able to execute for another VM (or another process thread in a bare metal Windows/Linux OS) would be out of the picture. Even if it could, any advantage would have been lost and turned into a disadvantage as the L1/L2 cache would have to be flushed out and VMexits have to be executed (thus having negative impact to at least two VMs).
@IRIX201110141
As far as the L1TF scheduler, I suppose you are referring to this bullet point from this KB https://kb.vmware.com/s/article/55806
Mitigation of the Concurrent-context attack vector requires enablement of a new feature known as the ESXi Side-Channel-Aware Scheduler. The initial version of this feature will only schedule the hypervisor and VMs on one logical processor of an Intel Hyperthreading-enabled core. This feature may impose a non-trivial performance impact and is not enabled by default. Please see resolution section for details.
It looks like it just means ESXi will avoid using HT altogether.