Hi there, my partner is a national level competitive power lifter.
I asked him and he said that whey protein is fine to take for type 1 diabetics, the main concern you would have to watch for is the addition of additional sugars to make them taste better. Would have less of an effect when taken immediately post weight training due to the translocation of glut4 from muscle cells (an action normally performed by insulin) which allows the muscle cells to take in glucose from the blood stem in the absence of insulin meaning the effects post training are likely to be less pronounced and less of a worry. (The same does not apply to endurance training)
the debate about high protein levels being bad for kidneys has never been shown to have any negative effect of those with healthy kidneys although can add additional stress to damaged kidneys.
I'm not sure about your question regarding injection sites and why whey protein would have any effect on injection site health?