Can oxygen help in treating carbon monoxide poisoning?

Yes. Carbon monoxide (co) stays tightly bound to hemoglobin, forming carboxyhemoglobin. Co comes off the hemoglobin gradually as the hours go by. Studies show carboxyhemoglobin's half-life to be about 4 hours (3-5 hr) in regular air, but about 1 hour (30-90 minutes) when breathing 100% oxygen for treatment of co poisoning. Increased oxygen makes the co come off the hemoglobin and leave the body sooner.
Yes. Particularly high flow oxygen (delivered by a face mask) as this will decrease the half-life (time carbon monoxide stays in the system) dramatically.