If you're asking if it would be a medication you could use in quarantine tanks as a preventative measure for new incoming fish, I wouldn't. It's usually better to quarantine new fish in just fresh, clean cycled water. If you want to be cautious and take the quarantine period seriously I would get a second set of nets to be used only in quarantine tanks and keep your nets in separate drip buckets. The use of a net soak can also help cut down on the chances of cross-infection between fish occurring.
Dosing antibiotics when there isn't an identified bacterial infection can lead to the development of antibiotic resistant bacteria. Although not bacterial, we're already encountering cases of Ich that are resistant to formalin, malachite green and acriflavine which may be due to their use prophylactically by breeders and retail outlets. Recently I've been suggesting people use the salt / heat method of treating Ich and if that fails or the fish are sensitive to salt to go straight for quinine sulfate.
Having said that, I just realized you were talking about Maracyn Oxy (I missed the Oxy part). Maracyn Oxy is stabilized chlorine and I suspect it would just stress some fish.