I don't see why not as long as the discus are large. Silver aros love planted tanks and the few I have had never ate any fish I had with them no matter the size.(3"jd's, 4"oscars,ect with 22" aros)
Do you have a discus tank? Are they adult discus? What size is the tank? Realize that arowana grow big quickly and you'll need an 8 foot long 30" wide 300g tank within just 2-3 years.