I can't think of anything they won't dig up. Any plants I've ever put with Oscars they end up swimming around with. You'd have to get something permanently anchored, live plants probably just won't work.
You can have Java Fern as long as it is already well attached to large pieces of wood or rock that the Oscars can't toss around. Same with Anubius & some of the Crypts. Don't have Java Moss, they will tear it to shreds.
Seeing as the Oscars are already in the tank, you won't be able to have substrate rooted plants. They need a couple of months to establish before the fish are introduced & there are a few other tricks that need to be employed as well, so they are not an option for you.