If Hagenbecks really try and enforce this policy they have been remarkably unsuccessful, with over 25,000 photos under the "Hagnenbeck" tag on Instagram alone. As for reviews there are over 7,600 on Google but only 2.000 on Tripadvisor. Of these 20 rated it as "terrible" with review titles such as "Horrible animal condition, we would expect better for Germany". Overall though they have a very good review rating on Tripadvisor and should be very happy with it.
Any zoo with a marketing department for the 21st Century wants you to post photos and talk about them. They will be spending most of their time discussing ways of getting more Facebook likes, Instagram posts and Tripadvisor reviews and anything else they can get online, including Zoochat posts.
These conditions are to make sure advertising companies don't use their images for free, or weddings don't clog up the park without compensation. They might be used to try and scare off the worst of the "PETA" type criticism. Maybe back in the 1980's somebody thought a ban on photos online might be a good policy to try and enforce. But it would be an insane zoo manager that tried to pursue zoochatters, let alone the general public, for posting reviews and photos in 2018. The only thing they would achieve would be to make themselves a laughing stock.