Jessey is right---stay away from the store feeders.
If you want to use feeders, I'd breed your own (guppies, Endler's, platies, and possibly even convicts would make good candidates). If it were me, I'd go with Endler's. From what I hear they breed like crazy, and they don't take up too much tank space at all. Cons might out-maneuver your oscar and end up growing to adulthood in the oscar tank.
You've got to think of it as a really long-term commitment...the oscar should live 10 years or more under the proper conditions. Why expose it to a fatal disease just for the sake of throwing a live store-bought feeder in with it? Breed your own feeders, gut-load them prior to feeding, and feed only as a treat (once every week or every two weeks). Or you could check out the mealworm colony thread in the DIY section, which makes for a nice supplement.
If you plan on upgrading by the time the oscar is about 8", then I'd go for the tiger barbs. Otherwise, skip them. The oscar will need the room.
BV