I am pretty sure the lip on the hub is there to transfer and support the weight of the vehicle onto the wheel. Removing the lip would mean the only thing holding the weight would be the bolts securing the wheel to the hub. This would not be a safe thing to do. The bolts have a small amount of movement built in to seat the wheel to the hub securely, USING THE LIP ON THE HUB. Removing the lip would allow for the wheel to not be centred on the hub and over time cause a flat spot on the tyre and in extreme cases, tyre failure.
Grinding things off the car is NOT a safe practice in this case.
It looks like either the spacers are not compatible with this hub, (the listing is for a VW Golf) or they need a recess milling inside the spacer to take the lip protruding from the hub, thus supporting the weight of the car.
Yes, grinding the lip off would mean the spacer would fit flush to the hub, but just think about the physics, if you then hit a large pothole in the road, the shock would be sent directly to the bolts and not distributed between the wheel support lip and the bolts. You stand a very good chance in losing the wheel completely through the bolts shearing, under the extreme shock transferring from the impact to the bolts..
And I assume you will be informing your insurance company of the fact that you have removed the lip from the hub before you drive the car on the road and the reasons why?? You will be telling them wont you??
If not, then I think you have your answer.
And the result, in the case of an accident and a claim where the insurance company, or the Police look into the vehicles structure in depth which reveals an alteration in the hub area and the wheel support, WILL render your insurance null and void and could leave you personally liable for injuries and damages.
Hope this helps.
