Radiant Aura only gives a visual clue that it has been applied on select mobs. It is either too hard to see on certain mobs, or does not appear. On some, it appears as a gold halo. On others it is a glow around the midsection, but most mobs show no indication that the buff is present.
Also, the enormous diameter of the skill causes all mobs in a very large area to be aggroed onto the caster. Unless this can be changed to not actually aggro creatures until they are attacked by a damage skill/spell, this will become a problem for people soloing or questing, and in dungeons tanks will have to taunt creatures off the caster.