I don't see the problem. He only mentioned one problem that they will likely start to attack people when population grows more. I take it that means they are actually not disrupting the local ecosystem. And i heard somewhere there are too many people already. Sounds like a win-win to me
Or why not just eat them? They sure look tasty to me. That ban on hunting will be lifted soon enough after there are too many.
Or breed a few generations and select for more docile temperament and bigger udders. Then use them instead of cows

Change the word hippo to human and you have a very interesting video. They clearly have ways to "deal" with the problem but I understand them not wanting to take that route because they're also a big part of the park itself.

#1 Cane Toads we introduced to Australia to eat sugar cane beetles, they have poisoned other species to extinction and has led to severe breakdowns in Australian ecology. have a look
https://en.wikipedia.org/wiki/Cane_toads_in_Australia#/media/File:Bufoinvasion.gif

austrian goverment introduced Javan mongoose to croatian islands around 1910 to get rid of Poskok snake (Vipera ammodytes) and snake population is still thriving around here.. they became friends.. eating chicken and ducks

they fucked up our intire ecosystem

#3 and #4 Made me think of Big Pharma.

#5 well , except this actually happened

I'd say kill em all
they're equivalent to the wild boars that feed on farmers crops here and what do we do?
Fly helicopter and shotgun em down before it gets bad.