Kind of a general question. Did you have any specific urchin in mind and what type or reef?
There are a few that will co-habitate just fine with corals. The main issue would be their sometimes clumbsy "bulldozer" movements through the tank. Mespilia globulus aka Blue tuxedo urchins (my favarite) are quite peaceful and not destructive at all. The only caution is not to add one to a new tank nor one that is "too clean".
Depends on which ones and what you expect them to do. The long spine urchin is a good algae controller, but may knock frags over. Others can be bull dozers to larger pieces. They have their place and you need to determine if they are right for your tank.
Personally, I like the black long spine urchin, and if your tank is healthy you'll never miss the corraline they eat as it will grow back quickly.