Aid comes in many forms, and I think some of them are definitely more prone to expropriation than others. Educational materials and vaccination would seem to be hard to turn into guns and troops. Food aid will be expropriated to at least some degree, but when it's necessary food aid is a life and death matter. We can let a few goons get fat off their Kalishnikovs if it saves half a million lives. Water typically comes in the form of purification equipment, I imagine (although I've actually no idea). Seems we should have somebody watching where this gets set up.

Money, vehicles and medicine (all sorely needed) would seem to be the most easily diverted. However, even there the benefit of a handful of vehicles or a truckload of antibiotics would seem to outweigh even the most serious corruption issues.

Corruption stems from a variety of causes, primarily lack of accountability on the part of government officials and an inadequate criminal justice system. Unfortunately, it doesn't seem to be something that can easily be cured from outside the corrupt society. The New Orleans Police Department has always been considered one of the nation's most corrupt, and the FBI (for example) has been unable to affect change.

However, I will point out that there is a difference in degree between official corruption in the United States and Africa. I.e. in the United States you get occasional ticket fixing and cronyism. In Africa you get army checkpoints set up for the purpose of relieving all passers by of their valuables.