It's always a risk jacking on a part that you don't know to be designed for it. They may be strong but it might not be strong enough in the direction required. For instance it's common for people to jack on suspension mounting points but
lower suspension arm locating points are not load bearing. The strut takes the weight and the
lower arms just locate it laterally. The
lower arm locating point is not required to take any vertical weight at all!
If you jack on a point like that and the area of the bodyshell bends or caves in? That's not an easy fix.
This is interesting and makes sense. There could be some kind of certification issue which stops VW stating that they are jacking points even if they are strong enough. How come they sell kits for them I don't know but there is obviously some bureaucratic reason behind it all.
The kits include parts for the rear as well so I'm fairly confident both the front and rear points are up to the job. I've jacked on the front ones many times, oil changes etc. I've not jacked on the rear ones as often but I have used them.
A block of wood on top of the jack is not a good idea as it would be too easy for the car or jack to slide off the wood. I use wood blocks but they are shaped to fit into the jack and axle stands and grooved to locate on te sills.