There are 2 reasons Oxyclean is not a good sanitizer option. We need to look at ingredients before I discuss these.
Sodium Carbonate - good cleaner, zero sanitizer,
Sodium Bicarbonate - good for baking (Baking Soda),
Sodium Percarbonate - good cleaner, fair sanitizer
Oxyclean contains both Sodium Carbonate and Sodium Percarbonate. The main difference between the two is Sodium Percarbonate is essentially Sodium Carbonate that contains hydrogen peroxide released when dissolved in water, and hydrogen peroxide is a sanitizer. So technically speaking, Oxyclean is a sanitizer, but, because Sodium Percarbonate is not the sole ingredient, and because Sodium Percarbonate then only releases small amounts of hydrogen peroxide anyway, and then hydrogen peroxide requires longer contact times with germs to kill them (far more than bleach and other acid based killers), Oxyclean should not be relied upon as a sanitizer.
Here's a tip: If you want to make Oxyclean an even better beer scum cleaner, add a small amount of Phosphate free TSP. I use Savogran in the green box. You will essentially have PBW.