Is Diabetes considered a blood disorder?

Hello and thank you for posting your medical query on E health Forum.
Diabetes Mellitus is a metabolic disorder where in a person has high blood sugar, either due to reduced insulin secretion or due to decreased response of cells to insulin that is produced. It is not a blood disorder.
Some common Blood disorders include conditions like hemophilia, von Willebrand's disease, Leukaemia, etc.
You might consider seekng a opinion of your GP while filling out the insurance form so that no errors are made while filling them out.
I hope this helps.