Giant danios generally do well with RV cichlids. I've had good luck with them with lower aggression mbuna, peacocks, most Tanganyikans, and non-piscivorous haps from any of the lakes. Obviously, you'll want to avoid putting them with the larger piscivorous species like the Malawi eye-biter cichlid, and you have to be careful with the hyper-aggressive mbuna (like kenyii and auratus) and Victorian species. The aggression of a fair number of Victorians (but not all) is easily on par with mbuna.
With any RV cichlid (mbuna especially) it's usually best to add the danios first, as then they are part of the environment when adding the cichlids and are less-likely to be targeted. When adding the danios after the cichlids are established, you'll need to watch the danios and remove them if they become targets. It's usually successful with non-mbuna RV cichlids if the danios are added later, but still watch. You also have to look at the stocking rate of the tank. If you are already pushing maximum filter capacity because the tank is overstocked to control aggression, adding a school of giant danios may not be the best idea.
WYite