The two benefits of the Channel Divinity are entirely separate
Another feature with similar wording is the Barbarian's 7th level feature, Feral Instinct:
[...] you have advantage on initiative rolls.
Additionally, if you are surprised at the beginning of combat and aren't incapacitated, you can act normally on your first turn, but only if you enter your rage before doing anything else on that turn.
These are not in any sort of "only if you have advantage are you not surprised" relationship; they are two separate benefits of the same feature. If these two effects were meant to be connected something would say so, or different wording would be used. In fact, surprise section shows us how they might word things that are related; you must enter a rage to prevent surprise. Nothing connects the initiative rolls to the surprise immunity the way that the surprise immunity is connected to rage.
For another feature where two effects are related we can look at Oath of the Ancients Paladin's Channel Divinity: Nature's Wrath feature, which does have different wording:
[...] As an action, you can cause spectral vines to spring up and reach for a creature within 10 feet of you that you can see. The creature must succeed on a Strength or Dexterity saving throw (its choice) or be restrained. While restrained by the vines, the creature repeats the saving throw at the end of each of its turns. On a success, it frees itself and the vines vanish.
The later effect only occurs while the first is ongoing. No such language exists in the Radiance of Dawn feature, so no such relationship exists. Radiance of Dawn has two completely separate effects:
All magical darkness within 30 feet is dispelled.
Each hostile creature within 30 feet must make a Constitution saving throw (and thus takes damage)