That would seem to be extremely unethical and possibly at least borderline an OSHA violation. If a workplace is claiming that certain procedures are being followed and they are in fact not being followed, I think plenty of lawyers would be happy to take that lawsuit.
As far as this being unethical -- maybe it is -- but since when has that stopped anyone? There are people still being forced to go to work sick because they have no way to take sick leave without losing their jobs.
At the end of the day, it's a lot less risk to HR to not piss off a couple of politically fringe employees over something that the vast majority of employees will do voluntarily anyway, without any coercing. Two unvaccinated employees out of hundreds probably won't cause a problematic COVID outbreak, but they could file a lawsuit.
But for the vast majority of workplaces, there's not much of an existing precedent to do this, and I suspect the vast majority of employers will not want to rock the boat too much. I suspect it'll be something that will be "required" by policies but not enforced in practice. The people who want to get vaccines will get them, and those who do not will ignore the policy without repercussions.