Those are 2 different things. Typically, O2 is added prior to/while you add yeast, so that the yeast have the required oxygen.
Degassing is the process of shaking, stirring, etc to release CO2 after the fermentation process has begun. Co2 inhibits the yeast from performing their jobs to the best extent possible. I am a new mead maker and I am amazed at the amount of dissolved CO2 in solution in meads!
I never degas my meads. I guess it's because they've been around for a while, and the co2 has long disipated out through the airlock. I rack them occasionally when they need it, and top up. If your mead is gassy, there would be a big benefit to degassing it before bottling. If not, there wouldn't be a reason to degas.