Both worked in another medium before taking up photography. Atget was unsuccessful as a painter.
Both would be considered eccentric. For example, Atget lived on bread, milk and bits of sugar considering all other food as poisonous. He always wore the same rusty black coat as he worked.
Both were only recognized very late in life.
Both were championed by some one else. In Atget's case it was Bernice Abbott.
Both used very primitive or old equipment. But Atget had much better technique.
Both have now been panned on APUG. A rather dubious distinction.
Personally I much prefer Atget's work.
Atget has a crater on the planet Mercury named for him.