UVs on shields do very little in general and there are very few if any situations where you're going to be taking surprise shock damage where you would want dragon scale... I'd probably try for normal max to tank thwacker hits slightly better during C42, since that's the main area you'll be using it in.
If it's still at 3* you can make omega shell out of it. My omega shell has shock med and while it doesn't make the biggest difference at all it's not a bad UV there either since shock is particularly bad and any advantage is a good thing.
Someone may need to correct me as I'm not 100% sure on this, but it has been my understanding that status UV's on shields are vastly inferior to the sheild's native status resistance. What I mean by that is even a MAXIMUM! Shock Resistance UV on the Dragon Scale shield will not have as strong a resistance towards Shock as a non-UV'd Grey Owlite Shield. That being said, I'm sure the shock UV will make your Dragon Scale shield a little more well rounded, but if you really want good shock resistance, you should get an entirely different shield such as Grey Owlite or the Crest of Almire.
To answer your question about whether your choice in shield should be based upon its health, I think you should choose your shield based on its native status resistances or its offensive bonuses. If you choose a shield based on status resistances, the easiest and most efficient way to cover the most important statuses is to get the Grey Owlite and Dread Skelly shields. Otherwise you could look at Barbarous Thorn Shield for the sword damage bonus or Swiftstrike Buckler for the massive attack speed bonus in exchange for a weaker shield.
I should add that your choice of Dragon Scale shield is not necessarily a bad choice, and is in fact a fantastic shield especially for running the Compound 42 Danger Mission, but it is going to be difficult for you to cover every status type without still crafting a Grey Owlite and Dread Skelly shield.