If we look at the idea that increasing oil content raises compression because more oil takes up more volume in the combustion chamber then for all practical purposes it's myth.

First up, oil out the exhaust equals oil in through the carb (assuming none of it burns so let's call it castor ). So how much oil could there be? If you look into the venturi while the engine is running it seems as though fuel/oil is pouring through. But the engine has turned hundreds of times while you glance in so we need to know how much oil passes through the spray bar every cycle because this will be the volume available. This is easy to work out. All you need to know is the total volume of oil in a tank, run the engine full throttle and note the rpm, note the time it runs on that tank and you have everything you need. Run time by rpm gives the number of cycles. Divide the number of cycles by the oil volume in the tank and there's your answer.

As an example a 300cc tank with 20% oil has 60cc of oil. An engine runs at 10,000 rpm for 10 minutes on that tank so it turns 100,000 times. So the rate of oil flow is 60cc/100,000revs or .0006cc of oil per cycle. Now considering your average largish engine like a .60 has a roughly 1cc combustion chamber then your compression won't go up by much if the volume is reduced to .9994cc. In fact if the engine in this example was a 10cc (.60) then it's dry compression would be 11:1 and it's wet (with oil) compression would be 11.006:1 which is completely unnoticeable.

Of course if the OP was talking about raising perceived compression with more/thicker oil then I've done all this for nothing