I'd want a lot more info about his abilities and limitations before making any recommendation(s). Stuff like fragility of bones, how much weight he can hold, for how long, amount of force he can exert in a hand squeeze/finger squeeze, arm length, symetry of arms or specifically how arms are asymetrical both in length, strength, range of motion, general bone health in arms, back, shoulders. Also info on how recoil may effect bones - especially in the hands.
This is stuff a doctor and a physical therapist/rehab expert would be needed to obtain.
Do not take any of the above as discouraging your friend from shooting. There are ways around any situation. I can't find the cites, but there is a guy with no arms who shoots pistols quite well, and a blind guy who convinced a judge it was safe to issue him a concealed handgun permit. There are programs (VA, Americal Legion, VFW) that take vets with all sorts of disabilities out shooting - bullseye, benchrest, trap/skeet, bowling pins, just plain plinking.
Feel free to PM me if you want to discuss this some more.