After looking at the other pictures of the exhibit(s) posted here, it appears that the zoo used all the expected plants to deter okapi browsing. I suppose, as you say, this enclosure looks so good in part because the animals haven't had enough time yet to clear it
This also demonstrates another difference among zoos: there are plants here that some zoos use because animals don't usually eat them...while other zoos' vets ban them from enclosures because they have toxic properties
