This depends on your approach to keeping them.If you just go for big aggressive cichlids in medium sized tanks, then yes you are likely to have casualties.
If you try to keep notoriously aggressive fish like flowerhorns in these communities then the likelihood of casualties is even higher.
Personally I hate the thought of fish dying due to my poor judgement,or just because I don't have the self control to admit to myself,this combo is risky,but so what,I want those fish.
There are enough cichlid and non cichlid fish out there that are perfectly compatible for every size of tank.There is also a wealth of information on the Web and forums like mfk.
The only things needed apart from the sources of information mentioned above is compassion for living things and enough self discipline to make the right choices.
This viewpoint has nothing to do with being a purist nor does it have any bearing on my view of flowerhorn compatibility.