I would think that you would need to have specialy clearanced dies based on the thickness of the material.
Every louver press that I have witnessed in use is set up for 18 to 20 gauge steel or .050 alluminum.
I don't think the actual cut side would be a problem, but the back side (curved) part of the louver might be.
Most license plate covers are very thin material.
In any case, I would try it out on a scrap first.
Being hydraulic presses, you might be able to drop the pressure way down but keep in mind that a louver press does not work like a shear, cutting from one end to the other, but strikes the female die evenly all at once. JMO, Bob