well, it would depend on a lot of things. if you had a large tank say 90 gallons and you had a group of discus, either only 1, a breeding pair, or a group of at least 6, and 1 angel or a group of about 5 or more, then you should be okay. both of these fish can be aggressive when kept with just a few of each other. having a group would spread out agression. also, i would watch the discus and angels at feeding time since angels are a bit more "aggressive" eaters and discus will pick at thier food until satisfied. other than that they are compatible.
*** heard the biggest problems keeping the two together were at feeding time as mentioned above, the different water hardness they prefer and the different water temps they thrive at. While they look great together, they dont usually seem to work.