I swear, the longer I'm on YT, the more I think that yorkies are prone to skin issues more than anything else, ya know?
I think it's tough to answer your question as to whether the D.earth would work. What are the symptoms you're seeing and how long? What are you feeding? Is it worse at certain times of the year?
Depending on the cause, sometimes giving fatty acids can help - I use one that contains fish oil (the EPA/DHA), GLA, LA, and vit a/d/e. But it all sort of depends on the cause.