Clutch of Dragons, I believe, has a Drake 'Day Bag', that is essentially a body armor bag for their drake form, which is used by Ryan Mercury and company.
As for Dragons (especially Great Dragons) using something like worn armor? Not bloody likely, not until MUCH later in the mana cycle. Even though it might help, their dragon pride would prevent them from doing something like that, unless there was a threat they recognized as an equal (or nearly equal). And it would be bad form to use it for dragon-on-dragon fights. So no, no dragon armor until we have weapons that can reliably hurt dragons.
As RHat said, anything that can punch through a great dragon's armor isn't going to care about the few extra points of armor, and it would be a sign of weakness to rely on that, rather than spells and your innate abilities.