i think Ms. Duck's explanation makes the most sense.  We have WoJ that Erlking is only one of several beings that can call the wild hunt.  Given that this is also true outside the dresdenverse (in early mythology) and that in early mythology Odin is one of those beings that can call the Hunt, it's reasonable to assume Odin has that same power in the dresdenverse.  Add to that Erl's comment that he messes with those who messes with his hunt and you have a reasonable cause for Erl to mess with Odin's plans, (i.e. Marcone).  Add to that Erl's domain is on the other side of the FBI building and you now have a pretty solid case for it being Erl.  Plus the magical item here turns people into one of the greatest hunters known to human kind, that right in line with the way Erl likes it.

Also, I would like some sort of zoom-to-event function.

Looking at the API and seeing that it's open source it seems like its feasible to add whatever you want, worst case scenario you just add standard links below the rendered timeline that link to specific areas.

I'm tempted to get into it but am too busy right now with full time work and school plus 4 kids.