Middle fingers on right is almost 100% numb and has an injury on rotator cuff on shoulder of opposite arm. could numbness be from compensating for pain or from injury itself?

Uncertain: These may be two separate issues. But now It could come from carpel tunnel, or a C7 injury.I don't think it's related to your rotator cuff injury

No, yes: Numbness in the fingers is not likely to be related to a compensation for a rotator cuff injury on the opposite side. It can be related to an injury or even the same injury. A "pinched nerve" in the neck (cervical radiculopathy) or at the wrist (carpal tunnel syndrome) are among the most common causes.