So I'll try to address all the points in one post.
Persistence hunting - no they use the bow and arrow. The idea of hunting through persistence running was first put forth by Harvard anthropologist Dan Lieberman. My professor, Henry Bunn, along with another professor at my university, Travis Pickering, pretty much debunked that hypothesis as the method of hunting in the paleolithic through the use of mortality profile analysis. Here is the PDF of the paper they wrote in the Journal "Quaternary Research":
http://diyhpl.us/~bryan/papers2/paperbot/Bovid%20mortality%20profiles%20in%20paleoecological%20context%20falsify%20hypotheses%20of%20endurance%20running–hunting%20and%20passive%20scavenging%20by%20early%20Pleistocene%20hominins.pdf
The Hadza nearer the roads do use money, but the ones in the bush do not. These bows are largely obtained through trade - a t-shirt, a pair of sneakers, or some tire sandals, or maybe a bunch of six inch nails which they use to make their arrowheads - that kind of thing. Other groups trade more directly with Tanzanian currency, like the Maasai for example.
Giraffes are not infrequently killed by the Hadza. That is the largest of their routine prey animals. They certainly don't make a giraffe kill every day, but they do kill them frequently enough to use their parts for tool-making. They also kill zebras pretty frequently, as that is a favorite meal for them. But they'll kill pretty much anything smaller than a giraffe if it gets in front of their bows - including lions and other carnivores.
The bow is, so far as I know, not made from a sapling per say. It's more like a medium-sized tree that they cut down to the dimensions they want with ax and knife work. I'm not positive exactly on tree selection. I've seen some stuff on youtube, but I haven't had a chance to get out there myself yet. This summer will be my first one in Tanzania (couldn't be more excited).
I'll definitely post pics and probably videos. One of my research plans is to bring a 3D archery target to the Hadza and have them shoot it at different ranges so I can assess their accuracy. I'll definitely get video of that.