Floating plants can work, just be sure there's an area free of it so that you can feed the oscars. I had floating water hyacinths in my tank and my oscars didn't mess with them.
Depends on the type, since oscars are omnivores, anything tasty will be eaten, plants like water sprite probably won't make it, as stated above water hyacinth, penny wort (Hydrcotyle), or water lettuce may be left alone.
The hard part about hyacinth and lettuce is getting them enough of the proper wave lengths of light, and location of the lights above the water, and plants.
I never had much success with hyacinth indoors, except in sumps sitting in a window box.
One of my favorites with veggie loving cichlids, although not a floater, is umbrella palm (Papyrus), but only in a room that gets at least partial sun.
One of the great things about papyrus, is it can work well as a pond plant, in aquariums, and sumps, or even as a house plant (dry). In my ponds it would reproduce so fast I gave large bunches away every fall. The only fish I had that would eat it were Cincelichthys bocourti, and pearsei.