There is, but I think I should do the zoo justice to say the cage is slightly bigger than it appears here - it's around 20 feet high so in total volume it's not that bad (though obviously not that good either!).
When I visited in 07? this housed vultures, eagle owls and pied hornbills. The gibbons were on an island in a lake and in a few other cramped enclosures.
When I visited in 07? this housed vultures, eagle owls and pied hornbills. The gibbons were on an island in a lake and in a few other cramped enclosures.
There is still a gibbon island (with additional gabriellae) but I've got a feeling I read that this is more recent than 2007 (2011?) so it may be a different island - there's a photo here (I don't think I have any that show the setting more unfortunately): http://www.zoochat.com/1779/gibbon-island-saigon-zoo-16-03-a-270432/
All the birds you mention are still at the zoo in other exhibits; unless something's been demolished I don't think there were any cages that would have been better than these for the gibbons so it seems they've been moved to the best place for the time being.