The only zoo outside the continent they are native to that had Proboscis Monkeys is Apenheul Zoo, which stopped being the case in about 2015: https://www.dutchnews.nl/2015/06/apelheul-zoo-sends-surviving-proboscis-monkey-back-home/

These are rather interesting primates in terms of what they’re known for, worth seeing outside of Asia, although some zoos in Asia that have them are in countries they’re not native to. Basically I see nothing wrong with zoos in North America, Europe and Australia starting to have Proboscis Monkeys, no different it would be from taking care of other kinds of monkeys with similar situations.