As far as I can tell, which may not be accurate:
Defences are for the specific item.
Resistances are specific.
Offensive bonuses on armor are universal.
Offensive bonuses on weapons are specific.

Two different weapons with UV:low:construct are each still low construct. However, a cold iron vanquisher with UV:low:undead would be the equivalent of veryhigh:undead.

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Edit: Er. Looks like resistances are for the specific item too. Shield resistance doesn't kick in unless the shield is activated, evidently.

Judging from the stats on my own shield, I'd have to say no: UV:Normal on a shield modifies the shield only.

http://imageshack.us/photo/my-images/691/owlitecomparison.png/
*Images modified slightly. The top one is my L10 UV:Normal shield while the bottom one is a default shield pulled off the recipes tab, with the Normal bar filled in to L10. The red lines show where they match up to each other's line.

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Also, you can check what's going on if you go to your character menu: when I mouse-over my Avenger, it shows CTR:Medium, ASI:Medium and UV:Undead:Low. The CTR is from being L10, ASI from a Vog Coat and the UV is the UV. Similarly, my Shivermist reports CTR:VHigh: +2 from being L10, +1 from a Heavy Demo Helm and +1 from a UV.

From the wiki: Shields have defense and health, just like a player. When a shield blocks a hit, any damage that gets past its defense degrades its health. Once a shield reaches zero health, it breaks, leaving the player open to damage. When not in use, the health of the shield will regenerate. Note that the damage resistances of a shield only apply when the shield is in active use.

A shield with UV:Medium:Normal means the shield can take a few more hits from normal damage before breaking. Armor with UV:Medium:Normal means that when you take damage from normal, you take slightly less.