Had a friend who put in an angel with discus and it didn't work out as the angel was aggressive, but other people on the forum have kept angels with discus.
I think it is trial and error, do you already have the angel or are you considering buying one ?
If you already have it then try it but keep a close eye on them, if you don't have it then why risk a full out war in the already established tank with a fish you might have to return to the shop
I wouldn't recommend it. Angels tend to be more aggressive than Discus and, since both inhabit the same tank areas, you could be facing serious bullying or fighting.
P.