Think about this for a second. If you're just talking pressure drop, the only thing that matters about air filters is the surface area (bigger = better), and porosity (more = better). So given a filter of a certain size, how can a filter be less restrictive? The answer is that it must be more porous. Period. . Which means that more contaminants have to be making their way through.
As far as I'm aware, there isn't any magical fairy oil that manages to attract dirt, or "pull more air", no can it "make air more dense". No matter what media we're talking about (paper, cotton gauze,rolls of toilet paper, etc), if you oil it you add density which can hold more contaminants. But once those contaminates begin to accumulate, they and the oil will begin to "choke off" the air channel- same for an un-oiled filter.
The biggest claim to fame for oiled filters is that you can wash them and reuse them. And once you do that, did you oil it too much? Not enough? Who knows? I'll stick with a dry filter and throw it away when it's dirty. Truth is, neither is worth even a couple horsepower, unless incredibly dirty.