Garmp,,
Surely at some point you'll get a response from someone who has actually tried this, but in the meanwhile my "opinion" is the same as Don's.
I use the regular pads under my leveling jacks, and the jacks are capable of putting quite a bit of pressure on a fairly small area of pad under the right conditions (softer ground, etc). The pads are very tough, solid, flexible material and will absorb that pressure without a problem. I don't have the stackable blocks to compare, but would be concerned that the material and open design wouldn't take the concentrated pressure without failing.
Hopefully someone with direct experience can provide definite advice.
Mike