The old adage about loaded weapons comes to mind here: Perfectly safe until you forget they're dangerous.
Charging gaseous O2 bottles should be a simple process if common sense and the relevant precautions are followed. Added to authorisations once the correct procedure has been overseen by Inspection and Quality Departments.
I've never worked with LOX but imagine systems are best replenished outside due to the increased amount of contamination in hangars and the limitation of fire tender access. Somebody more knowledgeable will no doubt be along shortly.