Girlie was also wild born so Charlie is a first generation male.@Zoofan15 - Auckland Zoo staff have also told me that Zabu was wild-born and that added to Charlie's genetic value (possibly his mother Girlie was also, but I am not sure about that). Some of Zabu's surviving offspring have been determined to be hybrids, also - I always thought that Mandai Wildlife Reserve never confirmed the paternity of the iconic Sumatran orangutan Ah Meng's hybrid daughter, Medan, but an Australian friend who knows the Singapore orangutans well has informed me that Zabu did indeed sire Medan (and also, unfortunately, Medan's son Budi).
I've wondered if new import Daya was chosen because, not only will she soon be old enough to breed with Charlie, she will also still be of prime breeding age when Bahmi matures, should the unthinkable happen and Charlie passes away. and Auckland Zoo therefore decided to retain Bahmi as breeding male.
I'd say your probably right with that assumption. Charlie is entering his 40's and not many males have reached their 40's. Hopefully Charlie is able to have at least one offspring with Daya, but after his eventual passing, Bahmi would obviously be a suitable mate for her and her offspring (if it is a girl).
Long term I'd assume the goal would be to use Bahmi as their breeding male; he's very valuable and his mother, Melur is in her mid 30's so there's also a chance Bahmi will be her last offspring (especially with Charlie ageing). New females could also be imported to breed with Bahmi if desired.