hau Sherwood, That material (cubes of rotted
wood) will be great in a hugel.
That's the result of mycelium having done their work of breaking down the cellulose so what you have are nice little bundles of humus that will readily soak up
water.
What is left is full of bacterium that will eat the minerals and thus make them available for your plant
roots to suck up, absolutely wonderful stuff for any garden bed.
It works a lot like bio-char once down in the soil.
Redhawk