My Oscar lived peacefully with my Roseline sharks, for about seven months.
Then one fine day out of the blue with no warning, she ate one.
So like others have said, if it fits at some point in time the Oscar will try and eat it.
I switched to Silver Dollars and guess what, she tried to eat one of them as well. Only thing that saved it was it was too tall for her to swallow it...
Both of these fish can cover the distance end to end of a six foot tank with a single powered flap of thier tails. Yet the Oscar still managed to eat one and almost eat the other.
If you are dead set on it, try it but don't say we didn't warn you when you wake up one morning with missing Tiger Barbs and a giant grin on your O's face and a giant bulging belly.