All that does is change the way the damage is displayed. There isn't any difference in absorption between dagger and dagger-with-shield.
I just did a quick test using the Bloody Dagger (5-10) and my cleric, who has a shield. My listed damage is 7-13.
With Shield:
7 damage, (2) absorbed
9, (3)
8, (3)
10, (3)
7, (2)
Without Shield:
3 damage, (1) absorbed + 4 damage, (1) absorbed = 7 damage, (2) absorbed
5, (1) + 5, (2) = 10, (3)
4, (1) + 5, (2) = 9, (3)
4, (1) + 5, (2) = 9, (3)
4, (1) + 4, (2) = 8, (3)
See, the total damage + absorbed is the same, whether it's one attack or two. If that's his only reason for wanting a shield, then he can, but it might not be the best use for an attribute point.
