The situation with the spider monkeys is/was (circa early 2000s) that essentially the population was split into two management groups: the golden/Nicaraguan type and the dark/Mexican type. While the much larger golden population has alot of question marks regarding known ancestry, mostly from various US importations, the dark population was actually well documented and could be easily traced. The original imports were (again if I remember correctly) from the US, and went directly to Dubbo and Orana Park in NZ. These were unrelated until a pairing was made from one of each at Dubbo (at least this was the plan when I was last keeping up to date). In my mind the ZAA should have focused on maintaining both types seperately with a particular focus on the dark/Mexican group.
By mixing up populations and creating cross-breeds, the ZAA are saying the spider monkey population is worth nothing beyond a display animal. No animals will ever leave the region because other regions will not touch them. A similar situation was tabled for zebras, and already mentioned squirrel monkeys. I fully appreciate the difficulties that Australian zoos pose with imports, but I think it will be a decision that they will rue in the future.