can oscars eat bits a slatwater fish meat?
or is it too oily?

sometimes, i gave my oscar bit of squid and yes,
bit of salt water fish. they just grab them so far.
the only problem is that it make my tank cloudy due
to the fresh blood and make my tank smelly.

You could try bit of salmon, or squid as Paul has mentioned. However, I prefer to stick to what is available at the fish stores.