This is similar to how the setup was tested for the performance whitepaper on the legacy version of FT that can be found here:
I cannot think of a reason why it wouldn't be supported without a switch in the communication channel. The configuration for FT on the host is the same. You may have to come up with some creative ways to upgrade the hosts without a 3rd host. You will also give up the automatic remediation of FT due to a host failure. vSphere HA will normally restart a failed VM on another host and reconfigure FT sync for you. Without another place to run the VM, you'll be left in a reduced redundancy state.
TL;DR: Will work fine and be supported, but you'll lose some things.
Good to see that the VMware lab guys have done something similar in the past - that gives me an extra bit of confidence. I take your point about there being some loss of flexibility when it comes to rolling upgrades and maintaining redundancy levels during a host failure and I'll pass these points back to the end user.