Many know that there aren't many fish to go with oscars and so when they start an oscar tank, most hope that their tank is established properly when purchasing an oscar. Most tanks, people will buy some inexpensive fish that they intended to put in their tank in the first place. Obviously, with oscar tanks. Many only want an oscar in it.
The way to check to see if a tank is established is to put some feeder minnows in the tank. If they survive, put the oscar in the tank. The oscar will eat the minnows and be in an established tank by himself.

Oscars do fine with many other south American cichlids providing the oscar is introduced last, My tiger oscar is over a foot long and happily lives along side a jag,bp,gt, and two bn plecos all of witch would of fit in his mouth a few years ago. And as for your method of putting feeder fish in to see if the tank is cycled well that's a bit lazy and inaccruate lol. the more effort you put in to cycling a tank the better your fishes health will be.

Feeding oscars live fish is bad IMO for two reasons. 1 there to fatty and this makes it very hard for the oscar to digest. 2 It also makes oscars very aggressive.

__________________
Remember people the solution to pollution is dilution... weekly water changes!

Yeah, I really wouldn't recommend allowing him to feast on the minnows. Especially if they're the bait-shop kind. I can't imagine those are in perfect health and disease free ;)

Yes, I know that feeding live is bad for them. On top of all of that, they can get a disease called hole in the head. It's just a way to cycle the tank.