There were unsuccessful attempts to (separately) mix diana and colobus monkeys with gorillas at Port Lympne. I believe males of each species were killed by the silverback. The small primate cage connected via a now unused, overhead tunnel to 'Palace of the Apes' is perhaps the only remaining indication of the intention to mix other primates with gorillas there, however I believe the attempted mixings occured in the former chimp cage rather than here. At Howletts, the mixings were more successful (as in, the monkeys survived), and I think only took place in the newer gorilla complex. Howletts have held both greater and lesser spot-nosed monkeys, but I believe it was only the lessers that were mixed with the gorillas. An elderly pair were kept in an off-exhibit cage I think at the back of the gorilla complex and one or both may still be there, given that this species is still listed on the park's website. I'm pretty sure the Samango monkeys didn't breed, but there seemed to be more of them on their transfer to Port Lympne (5 at some point), when for a while it was just a pair that were mixed with the gorillas at Howletts. The two guenon species were not mixed with the same gorilla group as far as I know.
More recently, Port Lympne was mixing a single black rhino with the baboons, and I *think* they may mix their agouti with one of the howler groups. Also the De brazza and colobus mixed exhibit seems to work very well there.
It was indeed Bristol that connected its De Brazza monkey enclosure to the gorilla island, although I have never heard of them having been mixed with the gorillas while they were there. Its a real shame Bristol chose not to introduce the drills to this enclosure instead of spider monkeys, I think limited rotational access to enclosures is useful for olfactory enrichment.
Similarly, while I have seen photographs of colobus in the main Gorilla Kingdom at ZSL prior to the bridge being removed, I have no knowledge of them ever having attempted to mix them with the gorillas.
I believe the anoa/macaque mixing at Paignton was short-lived and therefore not successful.
Woburn I think is one of the most interesting mixed enclosures, successful in part I'm sure due to the huge section of woodland available to the monkeys. I believe there were colobus at one point, before the drills, along with the patas monkeys and macaques which are still present? I think this is one of the few examples I know of where it doesn't appear as if the monkeys have been 'added' to an exhibit designed for ungulates or great apes. Given the precarious state of many African monkey populations in captivity, it does surprise me when declining, hard-to-breed species are added to rather busy mixed exhibits where cover and escape routes seem lacking.
I think the new okapi sanctuary exhibit at Doue Biopark in France looks sufficiently promising, given they have been allocated Hamlyn's monkeys for the exhibit. Does anyone know whether the monkeys are restricted to a part of the exhibit or do they have free range throughout its entirety?
Bioparc - Zoo de Doué la Fontaine | Videos
Bioparc - Zoo de Doué la Fontaine | Okapi Sanctuary