We do it once in a while with the thinner .015 magnetic material, not for vehicle magnets.... printing direct to it on our Mimaki JV33 and contour cutting (scoring) it on our Summa S-160T cutter.
It's a fiddly pain in the butt process though. Pretty much have to put both infeed and outfeed tables to support the magnetic on each side of the Mimaki so it does not grab on the steel machine panels, the print platen itself is aluminum so it glides fine on that. Also have to print with pretty much little to no heat and let it air dry for quite a while before cutting. Using tables it does not run across the pre and post heaters and too much heat on the print platen can cause rippling.
On the Summa cutter, all of the panels it goes over are aluminum so no worries with it grabbing on that but still need to put in and outfeed tables for it to really run through decently. The weight and stiffness of the magnetic will cause it to bow up on the platen if it is not supported semi flat in the front and back. Takes pretty high blade pressure and very slow speed. All that being said once you get the hang of it, figure out what settings work best for your machines, and use tables to support the material it actually works very well.
If we were doing a lot of it or doing it often I'd just get a cheapo Chinese cutter off eBay just for cutting it since it is pretty hard on your cutter.