Diabetes is considered a disability. There is a question that they can ask you "are you are to do this job without any accomodations?" or similar (for you HR people) ... it would be like some in a wheel chair - we all have one, it can't be seen.
My suggestion is that you never say anything about your personal diseases. If during the interview process, you reveal that you have diabetes and you are not hired and you feel that you were not hired because you stated you have diabetes, you could sue them. When hiring someone, I don't like that I am told about someone disease, because then, I have to be certain not to use that information as a bias. I never have, and am sure to never write that information down as a note.
Anyway... what employers want to KNOW about you is "can you do the work required and are you the best fit/person in the pool to join the team", end of story. At some point, you may want to share that you have diabetes and such, but you are measured on performance. I really don't care what a person has so long as they are getting the job done (beiing on time, no missed days, etc) - if your concern is that you will miss days of work because of diabetes, you probally need a more flexible job.
I have found that in my field, senior living food service, having T1 is beneficial and helpful to seniors and in compassion for others with long term diseases. In some cases I have told potential employers that i have daibetes as a "seeling" tool - and it worked. I have never missed a day due to diabetes related issues - but have to a cold, flu, doctor appt., etc - just like other pepole (sp)..