DeBrazza's + Mandrills
The two were originally housed together with the red river hogs (they were on my last visit in 2003). The only change that I am aware of to the original plan is that the male mandrill did not get on well with the hogs, and so (the last time I saw the exhibit ... a few years ago now), he was off exhibit while the hogs were out. Since they now only have 1.1 mandrills, I'm not sure if they've have to rejiggle how the animals work in the exhibit. I always found the DeBrazza's to excel in hiding within the exhibit (so they may have been in the mix), or if they were not working out, they may have moved them all over to the gorilla hillside exhibit.
Cheetahs
The last male passed away at the beginning of this year; based on the most recent ISIS records, there are now no cheetahs left at the Bronx Zoo.
Gorillas
There are two gorilla exhibits within Congo, subdivided in such a way as to make the division difficult to see. Each exhibit has a resident troop, and there may be some splinter groups off exhibit.