On the video footage there is no apparent sign of the fin - quite a large structure on a Herc. With the aircraft impacting the ground inverted you would expect to see the fin broken to the side of the empennage.
Regarding the LOx, it is mounted well forward and low down in the fuselage in the unpressurised area surrounding the nose gear, roughly under the co-pilot's feet. It has reinforced structure around it, is free of critical components and vents to the outside. On USMC aircraft the LOx is optionally armoured and the flight deck floor above is almost always covered with armour.