Before I developed diabetes I had a gallon pin because I donated pretty regularly. I had no issues with it per se, but I always took oj with me to guzzle after because I would have a blood sugar drop and get light headed. I started donating in my 20's and didn't start to develop type 1 until I was 46, so the blood sugar drop had nothing to do with my disease. This is a common issue with donating and is why, here at least they supply juice and cookies after.
So I think that could be a huge issue for type 1's to donate, I wouldn't chance it now. But donating blood wouldn't be high on my list of things a type 1 should do, unless it's an emergency. Besides I have to wonder what all that insulin I take would do in someone else's body? Curious about that.