Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
I would assume that Healthy and Def EVs are to ensure Zerarora and Dracovish (after Burn + Kee) doesn't 2HKO, 20 Speed EVs so it can outspeed Corviknight and other mons similar (so Tbolt isn't resisted after Roost), and not sure about the 20 SpA