Oxygen scrubbers? Do you mean C02 scrubbers? I have no idea. The should have something. 12 hours inside a can with five people without it wouldn't be good. I don't even know what the pressure inside the sub is. Given the relatively rapid ascent profile, I am guessing the sub stays close to atmospheric inside. If they ran higher pressure in the sub, your partial pressure O2 would be higher and your body is happy with a lower percentage of oxygen. Given what we know of the controls, I doubt there is anything they can do about that from inside. If they raised the pressurized sub, it would probably pop apart (those adhesive shell connections are dodgy against internal pressure) and everyone inside would get immediately bent (or worse depending on how high pressure was inside sub).would they have oxygen scrubbers??
I think canada sent a ship with a decompression chamber to the site. I don't see many scenarios where it would be remotely useful in this case.