User blog comment:FairyRaven/Fairy Tail Chapter 390: The Story of a Boy, Review and Commentary/@comment-117.195.32.112-20140627092139/@comment-117.195.32.112-20140627093143

With Capricorn and Zoldeo, both were alive. Zoldeo could use his own powers as well as Cap's (Btw, what is Cap's magic? The human thingy was Zoldeo). Here, Silver is definitely dead, the body is just a vessel. So I doubt that.

Could be possible if Keith had the power to not just create and control undead, but also resurrect somebody. Though why they'd need to resurrect Silver is beyond me.