Can an algae culture be used as a scrubber, sure. There are people looking at using power plant exhaust in conjunction with algae culture to help scrub the CO2 from the power plant emissions and utilize the CO2 to boost culture production in order to produce algae for biofuels.
As for algae needing O2, they produce plenty of it themselves while the lights are on. No need to supplment it. Added CO2 on the other hand will benifit the algae and lead to increased production via denser faster growing cultures.
Air without CO2 would greatly hinder algae production. After the algae pulls CO2 out because it is needed
