Welcome Neill!
Can you somehow find out what species of wood the belly actually is? "African rosewood" could either be bubinga (Guibourtia sp.) or one of several true rosewood species that grow in Africa (Dalbergia sp.). Either way, these species will probably all be dense and hard. That would make them a good candidate for a a belly, generally speaking. Hickory would be an excellent backing, so I think you're pretty much safe to go! I'm quite surprised you can actually get hickory in South Africa; it's not a really common wood around the world. If you can't figure out the exact wood species, your best bet would be to measure the specific gravity of the wood, and design the bow accordingly, with some margin of safety.