I've booked prepaid and postpaid rates with them numerous times, and even via http://www.hertz.co.za, the prepaid site of their South African franchise.

With Hertz.com, it sometimes does not automatically credit to my AF/KL Flying Blue account; with Hertz.co.za, it never does - but the AF/KL/Flying Blue website allows you to get to a Hertz website where with minor effort (some identification data for you, the rental and the rental date) you can claim afterwards—and then they typically do post within a few weeks.