In-cabinet power outlets flush with wall or cabinet?
The ruling factor is that the junction box must be made of an appropriate material.  Not particle board.  

If you have a junction box inset into the wall so it's flush, and then you put 3/4" of wood material above it, and use the long outlet screws to mount through that, then effectively the junction box walls are wood.  So if things get sparking or molten-copper-dripping in there, it sets the wood on fire. Whee! 

You may say "but they allow this with drywall!"  Drywall doesn't burn.  It's used as a firestop, actually.