Maybe not, but TSNs have a great habit of eating rays from the tail up, folding the disc like a taco. Pretty expensive feeders for a tank of big large pred catfish.Arowanas wont stop the rays getting food as long as you get enough food to the bottom they will be fine.
There used to a vid (on Water Wolves IIRC, CFC probably knows) of a TSN at a public aquarium just folding up a ray and having a nice lunch.Our tank has the Red Tail, Tiger Shovelnose, 2 x Oxydoras Nigers and a pair of Silver Arowanas.
I have heard about rays being eaten from the tail upwards too, the thing is, we are not experienced in keeping rays and I think they are a specialist fish that you need to know your stuff with before getting, so maybe in the future.
Clare