Firstly, you are not supposed to put that much oil on it. The rule of thumb is that you should put oil on the blade and then try to wipe it all off again. Otherwise the oil might end up being counterproductive. If the sword is dripping with it, the oil could just serve to trap dust and moisture and stuff that really eat the steel (moisture is not bad in itself, salts and acids are the real killers - which is why you must not use your sword to poke around in the soil). In the end, the oil on the blade should be spread so thin that you cannot tell it is there.
So the answer to your first question, I think, is no. You will not notice any difference in slipperiness. I suppose that there might be a measurable effect on the relative friction between two swords if they are oiled. But I expect it would require very finely tuned instruments to see it. I certainly do not think anybody would be able to tell the difference by touch.
Bear in mind also that it is not as if two swords will stick very firmly together in the bind to begin with. They slide quite easily along each other in any case, with or without oil.
As to the question regarding oiled plate armour, I am not sure that is even testable. We would have to have the same plate with the same amount of oil, struck with the same amount of force at the same angle repeatedly. And we would have to do so for a range of angles. And even then, we might find it hard to figure out how to interpret the data. But by prejudice, I would think it is mostly the force of impact that causes the blow to be deflected and not so much the smoothness or friction on the armour plates. But maybe it helps to pour oil on it, I do not know. It strikes me as a rather bizarre idea, though.
