Should the hands be used for absorbing the impact after a jump?
Your assumptions are wrong. Yes, riders do extend their hands and feet just before landing, but not to make the bike work more. They do that so they can make room for the inevitable hand and feet compression which will happen when contacting the ground. If you don't extend hands and feet then you only have:


40cm absorbtion of hands and feet compression
15cm absorbtion of fork and rear shock (on a 150mm travel bike)
2cm absorbtion of tyre compression


anything else is pain on the body and bike.

If you do extend the hands and feet just before touching the ground then you have:


80cm absorbtion of hands and feet compression
15cm absorbtion of fork and rear shock (on a 150mm travel bike)
2cm absorbtion of tyre compression


This video shows an extreme landing at 1000fps but it displays the extend-before-land technique very well: