Me.
I don't find it to be a problem at all, and PADI are pretty relaxed about it, provided your diabetes is well controlled and you haven't had a serious hypo or hospital admission recently. I'm sure the PADI website would give you the full story on that.
To be clear, I have never taken any medication for my diabetes, and my body seems to look after me pretty well these days, so I am confident of my physical performance when diving.
To be honest, it's more of a pain ensuring we keep our tanks certificated (or they can't be filled commercially where we dive) than it is considering my diabetes in any planning.
For those on meds, they may feel differently. I imagine T1s have to ensure they're in a good place, with levels maybe a bit higher than usual before diving, because I know diving makes me hungry, so I'm assuming that's the exercise coming into play
Good luck with it all.
Edited, to be more fulsome.