He's right...lot's and lot's of folks in the US have diabetes, i.e. Type II is very prevalent. Diabetes has to be very bad in order to get disability, and usually involves another body system like vision, neuropathy, etc.
The only medically determinable impairment that makes a different in payments is STAT BLINDNESS. Some who have diabetes also have blindness due to diabetic retinopathy - but the blindness has to be really bad as in 20/200 best corrected. So the answer to your question is NO..diabetes in an of itself has no impact at all. A disability in terms of payment is the same for any impairment...must keep you from working for 12 months (or end in death). In other words, whether it is diabetes, cancer, arthritis, depression, a stroke, COPD, etc...all the same under the main definition of disability (except for blindness).
The only exception I can think of would be something like "Anoni know this" pointed out above, which would involve changing the CATEGORY of your payments, from retirement to disability. In 30 years with Social Security, I can't recall ever seeing this, but I think it is theoretically possible. They won't let you do that unless you would get a higher payment.
Diabetes with nasty complications might be grounds for drawing disability, in which case they pretend that you have reached "full retirement age," and pay you the amount that you would have gotten if you waited to file until you were whatever the maximum age is now. Switching categories in that case would not be to your advantage, because you would already be getting the highest benefit possible.
Statutory blindness does not have a different benefit amount, as I recall - it is all based on YOUR work history. The thing about blindness is that there are different rules that allow you to work more on the side and still receive benefits.
With diabetes, they look for stuff called "end-organ damage," like renal failure, blindness, hearing loss, other stuff that is collateral damage that goes along with diabetes. Diabetes in itself is often not enough to get disability.
There has to be objective medical evidence that whatever condition you are alleging will either 1) kill you, or 2) prevent you from doing ANY "gainful activity."
The "gainful activity" part is where it gets rocky. Many people believe that if, because of illness or injury, you are unable to return to your previous line of work, you are disabled. Social Security takes the position that while you may not be able to do your former job, you are still able to do something else. And they will probably list a few types of jobs that you could probably do.
They don't care if that kind of job is available in the area where you live. That's YOUR problem.