It's not a lot different than shared overselling.
I would be very surprised if there were VPS providers that don't oversell.

If you look at the price that VPS providers are charging these days and compare it with the price of a Virtuosso license you will see that most wouldn't be profitable with some overselling.

I have VPS with a few different providers. I assume they are overselling but as long as my service is OK I have no problem with it.