You can take a rental car there, the track itself has no rules against it. Several companies in the area have specific cars for rent to use on the ring. But fo

You can take a rental car there, the track itself has no rules against it. Several companies in the area have specific cars for rent to use on the ring. But for a normal Hertz/Sixt etc rental car you can run into insurance issues if you crash. Because circuit / race / timed use is excluded and damage to the track is as well (which is common on the ring and expensive). Cars specific for ring use have insurance that includes it, but usually with a relatively high excess. Expect to pay the first few thousand yourself if you crash.