How does RESPeRATE work with a diabetic?

Resperate doesn't directly help with blood sugar levels. That aside, high blood pressure and diabetes are correlated... whatever cause one probably tends to also cause another. It is unknown whether successful control of blood pressure prevents diabetes from developing - but not entirely impossible.

As a device it should work just fine for a diabetic ... I can't think of any reason why it wouldn't.

On your remark that "high blood pressure and diabetes are correlated", does it also mean that people who had high blood pressure will likely have diabetes too (IMG:style_emoticons/default/sad.gif)

Those with high blood pressure are more likely than the general population to develop diabetes. However, it isn't a guaranteed thing. Many folks with high blood pressure that never get diabetes.
The same goes the other way around.

I suppose it can also would mean that if you have high blood pressure, you more likely to have diabetes than the general population. I don't think that probability is above 50% but I would have to check.

High insulin levels cause the blood vessel walls to stiffen. High insulin levels can also affect the regulation of BP.

High insulin levels are generally a precursor to full blown Type II diabetes. So you can have high insulin levels caused by unhealthy blood sugar levels and also have high BP but still show BG levels below the markers for diabetes. However once one is diabetic they have a good chance of also having high BP.