Garde was (is) indeed a Type 1 diabetic, and rode (and finished) the Tour several times in the mid-late 1980s. He was a teammate of Sean Kelly and Laurent Fignon, among others, and was known for being an all-rounder and strong team worker. I'm unsure if he ever rode the Giro or Vuelta, and about the details of his palmares.
As a fellow type 1 diabetic who started racing about the time Garde was racing as a pro, I was very interested to learn that he also had diabetes. I remember reading it in a short blurb in Bicycling magazine, but it seemed that Garde kept mention of his diabetes to a minimum, probably due to prejudices still floating around the pro peloton about limitations that diabetics were perceived to face.
Given the relative paucity of information about endurance sports and diabetes that I faced (at least here in the US) during the 1980s, it makes Garde's achievements that much more remarkable, and he truly should be seen as a trailblazer.
I'd be interested to learn what he's up to these days, if any French readers know.