What antelope/gazelle species are suitable choices for being fed compound feed by guests in zoos? And then I mean suitable species, both in relation to their size, dangerousness and dietary habits?
West Midlands Safari Park in UK allow/encourage public feeding of virtually all their ungulates in the free-ranging reserves. These include(from memory) Eland, Waterbuck, Red Lechwe, Congo Buffalo, Giraffe, several Deer species, Barbary Sheep, Nilgai, Blackbuck (though these don't approach the cars) and formerly Addax(moved to a separate paddock now). They warn not to feed the Camels though.
Eland in my experience, have been very friendly in my interactions with them. So have Wildebeest (patted one at Safari Niagara)!
...and Ankole Cattle. Which I know are not an antelope / gazelle but I find them completely terrifying! Far more than any of the others mentioned. The Nilgai are quite bolshy though.
Those horns are freaky! Also not antelope but in several parks/zoos there are opportunities for the public to hand feed giraffes. There's a zoo in my area about an hour and a bit away that allows the public to hand feed the giraffes and Eland and other hoofstock.
