Yes, all SliderPLUS versions can be used on an incline with the help of the Steady Module. Since the SliderPLUS v4 and older do not have a damping mechanism, the Steady Module must be attached to them in order to obtain a resistance for incline shots.
However, the SliderPLUS v5 does include a dampener, so it can be used with a Slide Module v2 or Slide Module v3 at an incline of up to 22.5 degrees with a camera load of 5 lb or less.
On the other hand, SliderONE v2 and SliderONE PRO v2 are both capable of doing inclined shots up to 90 degrees. You can check out SliderONE v2 page for the recommended weight load on various incline angles.