I'm not sure you're fully understanding what a pachyderm is...Not sure how “hot” this one is, but I consider gorillas to be pseudo-pachyderms.
Yes, they are obviously primates, but they are the most pachyderm-like of all primates: they’re large, grey, African, and herbivorous, much like elephants, hippos, and rhinos.
If a zoo doesn’t have “traditional” pachyderms, I think gorillas can fill a similar niche. Como, Franklin Park, and Santa Barbara all lack the “grey giants”, but have gorillas, so they feel like they have pachyderms.
Also, if a zoo has elephants, hippos, rhinos, and gorillas, they are either flexing their acreage or one of those giants is getting the short end of the stick exhibit-wise (Memphis with elephants, Denver with hippos, Cincinnati with… all but gorillas at the moment).
Manatees are something that can be considered more of a "pseudo-pachyderm," most certainly more than gorillas.
On the contrary, I'd say Brookfield has a pretty extensive collection of South American species: South American tapir, giant anteater, capybara, ocelot, coati, multiple primates, a plethora of rainforest and coastal birds, several dozens of neotropical herps, etc. It may not seem like it because these species are spread out across multiple different parts of the zoo, but it's much more substantial than you give it credit for here.The entire Chicago-Wisconsin area seems to lack any robust South American collections unfortunately. There are definitely certain popular species around but it is a blind spot across multiple zoos here.