While they are active, they can also radiate a single spell from a small list, which lasts as long as the (un)hallow spell is active. It is not clearly specified if this spell is to be considered instantaneous or lasting.
What would happen if an area dispel is cast in an overlapping area? (I'm thinking about temporary suppression of the linked spell but I'm not sure) Is there any difference if the area includes the (un)hallow altar or not?
While a 3e answer is required, I'd appreciate mentioning if the answer would be different in 3.5e.