I don't think oxygen is an additive as it is always picked up from the air. However, I don't think adding pure oxygen will help make a show mead get done faster - oxygen isn't what limits the yeast in show meads. Nitrogen, micronutrients, and pH drops are the real limiting factors for show meads.
Boiled yeast added as nutrients may violate the spirit of a show mead, but that is certainly debatable.
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