Left the zoo a while ago, so I figured I’d answer my own question in case anyone is wandering through wondering something similar in the future. Most of the species I was after were unmissable, or at least their exhibits were. I believe the last markhor probably either passed away or is BTS as of sometime within the last year - I saw where its sign would have been, now stripped bare. Grant's gazelle probably is gone. I think the muntjac is supposed to be visible from the train ride, maybe, but I didn’t ride the train so I can only speculate. White-headed lemur is totally unaccounted for, no idea where it may have been (not with the ring-tailed or either ruffed lemur I saw for sure) if it was even on exhibit or present at all. Klipspringer was a tricky one, I passed by a sign in front of no exhibit, then shortly after that another sign in front of a reasonably appropriate but empty exhibit, and then later briefly caught them sharing a small enclosure with a pair of king vultures of all things. The “urials” were signed as Armenian mouflon, but honestly I couldn’t get a good feel for what they actually were - I’ll upload a picture shortly. But everything else was plainly visible and exactly as advertised.
The biggest surprise was a pair of white-lipped tamarins, a species I can’t find any evidence for being kept elsewhere in the US. I didn’t realize they were such a rarity or else I would’ve tried to get better pictures - I only grabbed some quick ones to ID once I’d left the zoo. They'll also be uploaded momentarily.
There was also an unsigned reddish owl that I'm fairly certain was a Bubo species, but I didn’t take pictures as I had assumed it would be easy enough to look up once I’d left the zoo. Big mistake, because I’m really not sure what it was now, and it seems like another recent acquisition since there’s no documentation anywhere. The only owl here I can find evidence for online is the spectacled owl, which it obviously was not (and I saw elsewhere in the zoo anyway). Looking over pictures of the Bubo species, I’d say the closest looking one is maybe the pharaoh eagle owl? I realize that’s another major rarity within the US so I’m not going to make any positive claims on that one, and I’m not as good with birds as with mammals so maybe it just was a reddish Eurasian eagle owl or something. I’ve messaged the zoo about it though because I’m really curious now, and I’ll provide any updates I hopefully get.