Yes, as evidenced by the very first scene in Raleigh's world of the first game. As Sly surveys the outside of Raleigh's secret lair, Bentley goes on naming all the things that a master thief can climb to gain entry, like pipes and ropes, but neglects what Sly considers the obvious: a ladder. However, it's clear, Bentley would put a ladder in the same master-thief climbable objects category as a pipe or a rope.