I imagine this "refuge" like Yellowstone National Park. Maybe it is different, but I don't believe there is a fence around it with a gate.

So, if I want to hunt black bears near Yellowstone, I am legally permitted to setup a bait site (meat, donuts, blood, etc.) to attract a legal bear to shoot. If the bear crosses the boundary out of the Park, I am allowed to shoot him. If he's in the Park, I can't pull the trigger.

So is it unethical to take a black bear in that situation?

Does Zimbabwe have laws restricting baiting of lions? In the US, some states allow baiting for bears, others don't. Some states allow hunting bears with dogs, other's don't.