I think you did the right thing telling them. Surprise surprise the family covered for him for years - gives you a lot of insight to him. But i'm also guilty of enabling my son for a very long time - it took many people telling me i was doing him no good before it finally sank in.
At least you have transferred the burden of his safety to his family and away from you - that alone should give you some peace of mind. Sounds like they are willing to take the burden so its off of you. There - one problem solved.
For others reading - you may find my opinions on this situation very different then i would normally state but its because i understand what its like living with a type 1 diabetic. It is not a disease that someone lives with alone - it affects every person who lives with them. It is actually a very needy disease because the diabetic cannot always tell when they are having a medical issue and they rely on others to provide medical care when they arent coherent. when they throw addiction on top of it - its very confusing. You never know if its the disease or the addiction that is causing the behavior. Once you know what you are dealing with then you know the steps to take. My son acts the same exact way from low blood sugars as he does when he is drunk. He acts the same way on some other drugs as when he is having high blood sugars. The diabetic in them has to have help and deserves help - its not a one person disease - but if you dont know they are using you may mess up and help them the wrong way causing worse medical issues. Living with a diabetic is similar to living with someone who is bi-polar because they can have very severe mood swings when their blood sugars are low/high (in my case throw some teenage hormones in there and watch out). It would be unfair for anyone living with him not to know what was really going on.