hyperbaric chambers are indeed pressurized; they're mainly used to speed up the healing process on wounds, especially burn wounds...
they're also used to treat decompression illness as occurs with divers (caisson)
the use of additional oxygen in hyperbaric chambers is very dangerours since the oxygen under higher pressure becomes much more reactive and prone to enflame...
on the other hand you have oxygen tents; these are basically airtight sleeping bags filled with oxygen where athletes sleep in to be able to take up more oxygen in their blood... (they're obviously not pressurized (1atm)
Oxygen itself is almost always healthy to take; thats why in almost every scenario paramedics will give oxygen to patients.
Only for some people it's dangerous to give oxygen.
normally seen your breathing reflex is triggered by the abundance of CO2 in the lungs
but with some people it is triggered by the actual lack of oxygen.
so if you would give oxygen to these persons while they're passed out they will simply stop breathing because there's too much O2 in their lungs...