From my quick research on this, which is just that - quick - it seems that there are a few sources indicating that BCAA's, Leucine and Amino Acids in general all impair insulin sensitivity. There appear to be 1-2 sources that show it may help and not hinder. So there, you have your conflicting evidence.
I'm not a medical professional, but if this were me, I would look at it this way - what is the purpose of your BCAA supplementation? Are you training fasted? It seems the general consensus on here is that BCAA supplementation is of marginal value if your protein intake throughout the day is adequate AND you aren't training fasted. In a fasted state, you burn through BCAA's while exercising and may not have any in your blood stream to supply the demand, so your body may use muscle to answer the call - taking these around a workout may have some benefit in this case.
Again, I'm not a doctor, but given the conflicting evidence and some small jumps in logic, I would assume that if you are working out intensely, you are going to be improving your situation greatly from an insulin resistance point of view, and if you are doing so in a fasted state then any BCAA's you take will have a minimal impact on diabetes, as you are just trying to get BCAAs into the blood stream as you are burning them up. So it isn't like taking an intra-workout drink is going to overload your system with BCAA's and have a huge impact, in my small mind. Over doing it, however, may not be a good idea - but this could be said of protein itself in your case, since amino acids in general seem to impact insulin resistance negatively.
In other words, what stands out to me is that a lot of these studies are using leucine to avoid muscle wasting in sick people - not people who are getting exercise and creating a demand for these nutrients. If you are creating a demand, it doesn't make sense to me not to allow for a supply. Breaking down muscle for amino acids won't have a positive impact on insulin resistance either, and the aminos will wind up in your blood stream anyway, just from your own tissue instead.
Again, not a doctor, and I know very little - just giving my thoughts.