We can measure every aspect of the oil droplet because we're measuring it with trillions upon trillions of infinitely smaller and faster photons which give us a great insight without disturbing the structure. What would we bounce off of photons to get an equally accurate picture without disturbing them?
The analogy isn't a problem. The fact that there's nothing small enough to observe photons like we can observe the oil is a problem, but it says nothing about the integrity of the analogy.
In the analogy the water is space-time, meaning "observing" the droplet like we observe photons would require shooting another droplet past or into the first droplet.