The deadlift requires very little mobility. In fact, the majority of deadlift technique issues arise from needing to understand form more so than mobility limitations. The ability to effectively hip hinge, as well as some hamstring flexibility, is needed for the movement.
The hip hinge is the fundamental movement pattern that makes up movements such as deadlifts, cleans, snatches, and kettlebell swings. This tests our ability to lock in spine positioning while moving through the hip joint.