You can tell how saturated the shoes are after you have cleaned and then sanded them. When you sand them DO make sure you are not breathing the dust and DO make sure you are not breathing the dust from the inside of the drum housing. Depending on how old the shoes are, they may have asbestos in the shoes. Asbestos is not something that is good for you. One of the problems with oil on the shoes (besides being slick) is that it will cause the shoes to desentagrate. Depending on how your brakes are adjusted, that could cause you to scrub the the inside of the drum with the plating of the shoes. That would be a bad thing!
The worst thing that you could face would be buying a new set of shoes for your brakes. The lining of the shoes are pretty dense so it would take a little more than a few drops of oil to ruin them.