Is a kidney donation healthy for the donor?

Depends. A living kidney donor is undergoing a surgery he or she does not need and needs to weigh the potential risks he/she is willing to take. In the U.S., the mortality rate associated with the donor nephrectomy is 0.02-0.03% and the rate of major complication is 3-6%.
Caveat emptor. There is risk in everything but it truely is the gift of life.