That phenomenon, referred to as "crosstraining", has never proven to be an important part of rehab that is actively used in Physical Therapy. But your question about innervation is important, since it provides further reasoning for our approach. If the innervation is not damaged, the injured muscle belly is receiving 2 forms of signalling in the process of being used in its normal context: contractile signalling, which makes it fire the motor units involved, and pain, which acts to protect the area from firing. If the pain can be worked through -- because of a degree of healing, the use of light-enough weight, and the ability of the rest of the system to unload the injured component sufficiently to permit its motor units to fire anyway -- the area is worked, is bathed in accumulated lactate during the set (again, I've seen references to this, but I'm not sure of the precise mechanism -- it has been my experience that this is a significant factor), does not have time to scar down, and returns much more rapidly to normal function.
If the innervation is damaged, contraction is not possible due to the lack of an ability to fire the involved motor units. Homework: ask a PT how they "rehab" a scapular wing, and why this would work in the presence of the neurological defect that causes the problem.