I think when you look at the form or website, the question is likely to be "Have you ever been diagnosed......." The answer to that question is obviously yes. It will usually then ask for further information, like whether you use insulin, hospitalisations etc.
I haven't found T2 to be any issue for travel insurance, including for long trips.
Whatever you do, err on the side of caution. The point of claim isn't the time to argue your case with an insurer.