No, this is almost guaranteed not to work. Other members have explained why, I will just go into more detail why this will not work.
First, all male cichlids regardless of species are territorial. Some species exhibit this more than others, but it is an inherent trait of the fish that is programmed into their DNA and you are not going to change it, so accept it and provide for it.
Second, angelfish is a shoaling species, as is discus. In both cases they need a smallish group, at least five (never fewer, except for a breeding pair). Both will develop an hierarchy within the group once they are together, and this occurs fairly quickly in an aquarium, so this means you must start out with the intended group together, never add fish to an existing group of either species.
Angelfish and discus should never be kept together in the same tank. The fact that you do not see physical aggression does not mean all is well. It is not. Fish communicate chemically with pheromones and allomones, and you cannot see these, but the fish read them. Aggressive or dominant signals will cause stress to subordinate fish in the species, or to fish in other species. Angelfish are more aggressive feeders, which does not mean aggressive in the sense of physical fights, it means the angelfish are much more determined to eat any food placed in the tank, and discus are more retiring. Here again, you may not see physical signs of this, but it is there, and the fish are being impacted.
Individual fish can exhibit their inherent traits/behaviours to varying degrees. There is no such thing as a peaceful angelfish as such, it is merely the case that the individual angelfish may not be as demonstrative as another angelfish in exhibiting its natural behaviours towards other fish. It is always wise to assume the fish we acquire will be normal for the species. As soon as you risk the fish in the hopes the one selected will be abnormal, you are in for trouble.
The single angelfish you now have in one tank should remain on its own; if you add other angelfish you are likely going to see it being killed. It is certainly happier alone.
