Thanks, Wildlife Enthusiast. I figured out the problem, actually.
I realized my guests were saying "I can't see any animals from here!" So I thought, "Well, let's put a chimpanzee in with them and see what happens." And the guests didn't see the chimpanzee, either.
I looked and looked at my exhibit, trying to figure out what was wrong, because I could see the animals when I walked around in guest mode. As a last ditch effort, I tried changing the fencing to post and rope, and that worked! The guests could now see all the animals.
Turns out for whatever reason the guests couldn't see through one of the wire fences I was using from Martin1990's wire fence pack. I haven't experimented with all the fences yet, so I don't know if it's a problem with all of them. My guess is, I was using one with the stone posts, so maybe it was made out of the tall stone fence which I believe guests can't see through, and the code wasn't changed so guests could see through it. But I could be wrong, as I don't really know anything about editing objects, having not tried that yet myself.
Long story short, my saolas and pygmy hippos work now! :rolleyes