VenomousReptiles.org has an
article detailing an Atheris envenomation. While in my research I could only find a single confirmed death to an Atheris bite (which was in Africa with poor medical care) there is no antivenin. That should be an extremely important consideration before even thinking about any snakes in the genus. Having a protocol book (and forcing health care workers to actually look at it when needed) is an absolute must. Echis antivenin reportedly works on Atheris venom as well, but I haven't seen enough documentation on this to trust my life to it. Even if you could get some in North America, which would be easier said than done.
As with most species, try your damndest to avoid wild caught stuff. African bush vipers come in with all manner of strange parasites, many of which the normal dewormers (Panacur & Flagyl) won't even touch.
They are very cool, but extremely agile and are quite adept at hanging onto and climbing up the hook. Or grabbing onto cage edges, or anything else you happen to brush that very strong, prehensile tail near.
Ham