They get along beautifully with other birds. Of course there are always exceptions and some are grumpy little a-holes LOL
But in the wild they are probably the most naturally hybridising species of parrot I can think of. Galah x corella and even galah x major mitchel have been spotted in the wild. Galah x corella species are common enough I have seen a few in person.
They seem to fairly easily hybridise in captivity as well. Cockatiel x galah, sulfur crested x galah, little corella x galah, long billed corella x galah and major mitchel x galah are all currently advertised in various pet classifieds right now.
Photos from classifieds (note: these photos are for information only, I am in no way promoting the breeding of hybrids for profit).
Galah x little corella
(adult colour)
Galah x Long billed corella
Galah x cockatiel (don't have an adult picture available but they go orangish)
Galah x sulfur crested
Galah x major mitchell
(image is small cause ad no longer exists)
And a wild adult hybrid at a bird feeder... contrary to popular belief, they do indeed survive to adulthood but I have never seen them with a bonded partner.
In other news... I got DNA results back and my Manny, is a girl. She has been renamed "Mana" because I have been calling her Mana Bird anyway (we are gaming nerds).