No. The original post indicated that the MRI showed that it was an old stress fracture when they discovered it a couple months ago. It sounds to me like they found the fracture on an X-Ray and then did an MRI to see if it was acute. Many times a stress fracture caught that late will never completely heal unless something extra such as bone growth stimulation or surgery is performed.
If the physician decided that it was a non-union and wasn't going to achieve bony union he may have told him that he'd could go ahead and try to pitch as long as there was no pain.
However, we don't know that from the post and the only responsible reply is to tell him to see a sports medicine doctor or orthopedist unless he's gotten an OK to go ahead with throwing from his doctor. Personally even if he did get clearance from his doctor, I'd recommend he shut down, get a second opinion and look into bone growth stimulation as a preferred option prior to the last resort of surgery.