from the pistons moving down, its not a constant vacuum. you need a breather on your valve cover don't you? the vacuum is not at the bottom of the pan like with a pump. and if the rings are getting sucked tight to the cylinder walls which is the purpose of a vacuum pump for sure its drawing the oil to the bottom of the pan off the cylinder walls along with oil from the rest of the system. street motors dont get freshened like race motors do, that is why I believe running a pump on the street would result in a engine worn out prematurely.
