I can't say that I know for sure, but I wouldn't have thought so. The Polo is a bigger/heavier car, so the spring rates would be different if nothing else.
You know there are coilover option specifically for the Up! already right?
I wouldn't be quite so quick to judge. There is a lot of cross compatibility between various VAG group cars in regards to things like suspension. Most share common mounting points, but must have slightly longer/shorter struts, or have slightly harder/softer rated springs.
I know one owner on here, for example, is running 9N Coilover platforms and springs on the rear ofhis Up!
The front struts look very similar between the two cars, it wouldn't surprise me if they fit. Modding the Up! is still in its infancy, so no-one has really experimented with trying out different coilies.
If you happen to be able to lay your hands on a set of 9N coilies to see if they will fit, it would certainly not cause any harm to try. Then we'd know definitively!