I've never seen any proof of some mysterious illness that angels carry that will kill discus. I have done it with Kennys large albino angels. The only problems I experienced were that the angels are much more aggressive during feeding time. If you dont have some aggressive discus, they may not get enough food depending on how many angels you have. The other thing is that angels get very aggressive during adulthood and during possible breeding which doesnt sit well with the discus getting in the middle sometimes. Other than that, they never really bothered each other.