I have my uaru with a chocolate cichlid, some cons, an oscar, and a green severum, and I had to remove the oscar because he was getting picked on (and not by the cons). The uaru basically runs the tank and the severum is only 3-4" or so but had to go into the big tank because he was beating up the other fish in my growout (JD, FM, pinktail chal).
That's the thing with both uaru and sevs, they vary widely re: temperament. My other sev (a gold) is still in the growout, it's the largest fish in there and isn't aggressive in the least. I would add the sevs (or uaru) at a much smaller size compared to the angels, and have a backup plan in place.