A big angelfish may start eating rummynoses.
That would have to be one big a** angelfish. Rummynose tetras get fairly large when they are mature. Many people that keep discus also stock their tank with rummynose as they are a good indicator for water quality. Their noses will be bright red when the water quality is good. I would say that angelfish with rummynose will be just fine but I would add the rummynose first because if the angelfish are put in the tank first it becomes their tank and don't take to new guests to kindly.