First off, get familiar with the safety squat bar. I would suggest every training facility have one for athletes with injuries to the wrist, elbows and shoulders.
As well, you can still focus on scap retraction/depression work with the arms straight. Prone scap retractions would be ideal.
Yeah, you gotta give me some more info to help you out here. How long have you had the injury? What was the cause? What have you done so far to rectify things? The more info here, the better.
You can use them for all squat variations; however, I wouldn't use them too much with the actual pulls. The only area you would want to use these is perhaps from the knee-hip position to work on maximizing the explosiveness of this part of the movement. Remember, the first pull is more about getting set for the second pull than anything else.