It can be done. Probably depends on the aggressiveness of the first angel. I had a coral beauty in my tank for quite a while. Then my friend was getting rid of his half-black angel which I took and put in the sump for two months to check for issues. The half-black was kinda aggressive to my fishes in the sump so I put him into the DT. Of course the first week there were some torn fins between both angels, but since then, they don't even realize that each other is there.