The pocket tool can only do relatively simple faces:


but that stamp is easy to do with offsets. (the offset tool in sketchup that is, combined with centerline cuts)

you need 2 copies of the flat drawing and some way of referencing the safe area...
see here for the method of doing multi drawings:


I will do an example drawing for you just now and attach it here, the basics are
on copy 1:

1. remove the outline
2. add several offset lines starting at the stamp edge, the first one must be 1/2 bit diam away, the others can be more or less depending on what stepover you want
3. set the stepover lines as 100% deep centerline cuts
4. place the safe area for this drawing (this sets your 0,0 reference so it must be correct for both drawings)
   
5. set material thickness to 3mm
6. generate gcode to 'stamp1.nc'

on copy 2

1. place an outside cut on the outside edge of the object
2. set material thickness to 8mm
3. place the safe area for this drawing
4. generate Gcode to 'stamp2.nc'

use the Gcode joiner to join the 2 files together, stamp1 then stamp2 to create stamp.nc

It is/might be possible to do this in one drawing but a bit more complicated since you have to draw the offsets first and collect them in a group, then add the outside cut. If you ever need to change anything you have to do it all over again.

I drew a random shape and ended up with this: sketchup and nc files attached

 

more advanced ways of doing multilevel drawings.... (yes I know the sound sucks, I am not a voice artist...)