Gravity applies equally irrespective of the weight of the object
They are both being pulled to the earth at the same speed.
Would a ski provide lift?
Seems unlikely to me
Right except for the fact that the dirtbike hits the ground with more energy, compounded by the fact that the angle of attack is higher when it landed due to the lack of lift.
And yes, skis give them lift. They act as lifting bodies, which is why the record for the furthers jump is way further than that moto managed. As per wiki, ski jumpers below the minimum safe body mass index are penalized with a shorter maximum ski length, reducing the aerodynamic lift they can achieve.
http://projetmod.pnzone.net/rapport/ac/jbiomech2.pdf