It's important to note the difference in how protein affects someone with type 1 vs. type 2.
There have been several studies done on the matter which essentially found that excess protein had little correlation to hyperglycemia in people with type 2, but did with many people with type 1.
From memory, I believe the study found that excess protein DID help avoid hypoglycemia for insulin-dependent people with type 2.
Either way, excess protein DOES affect your body's ability to reach ketosis. However, it's still unknown exactly how our bodies use glucose sourced from excess protein, but it does seem to be used much differently than glucose sourced from carbohydrates.