I used to work in a place that made miniature bearings and even worked in the quality control dept for a while to.
No only would oil attract dirt they are sealed bearings anyway and not much of a way for oil to get inside with out taking out one of the bearing shields and clips. Which would not be to easy on bearings that small.
I even tried sewing machine oil to see if I could get it inside a bearing on a shot motor from a p2 and even as thin of an oil as that is. It still did not penetrate past the shield.
So I'm going to conclude that oiling not only is not really necessary its also not going to do much good on sealed bearings.