The core of an exploding supernova is not like a normal neutron star, especially if it is collapsing into a black hole.

The bulk of the energy of the collapsing core is emmitted as neutrons, as the core passes the electron degeneracy pressure maximum. At this point in the collapse, the core has converted into a neutron star, but it is still collapsing. When the neutron degeneracy fails, and the core collapses into a black hole, most of the kinetic energy is straight towards the singularity. There will be some angular component to the KE, which seems to be where you have a problem, but any assymetry to the anglular momentum will quickly be radiated away via gravity waves. This should smooth out the surface of the newly formed black hole. Any particles inside the event horizon have to be in a decaying orbit, and will eventually be sucked into the singularity in the black hole. the energy loss mechanism for this is gravity waves.

While this is happening in the core of the star, the rest of the star is getting blown apart in a type II supernova.