If my wife has little to no imune system should she breast feed?

Good & Fair Question. It depends what you mean by little or no immune system. Does she have a specfic diagnosis. Obviously her immune system is good enough to maintain and carry a pregnacy. I think even if her immune system is 'weak', what ever that really means, it would still be the best for the infant to receive the breastmilk from the mother.
Yes. Breastfeeding has many benefits for both mother and infant. Unless your sife has a serious medical/hematological disorder that requires frequent doctor visits and multiple drugs, i would still highly recommend breastfeeding for ~9 monthds (either direct or via breast pump).