Anecdotal, but from a friend (not wealthy) who lived near Jackson as a young adult the largest, most extravagant homes would not be considered vacant. He interacted with caretakers that lived permanently in one of the homes. This is especially important in the winter because temperatures can be so harsh in the Jackson / Teton / Yellowstone area. It was worth it to the owners to avoid any risk of a water pipe bursting. Apparently the caretakers told him utility costs alone for the McMansion were over $5,000 a month.

So clearly vacancy taxes can be gamed after a certain point of wealth. But I think they still would be effective at reducing the number of vacant properties because the bar to hire employees to exclusively live at your property to care for it is so high.

Incidentally my friend’s experiences in Jackson were influential in shifting him away from the libertarian mindset his parents raised him with. The realities of observing the wealth gap really troubled him.